I'm assuming the post was written by somebody who doesn't have an English Lit degree. They seem to be confusing two different things that sometimes overlap: Metaphor and Subtext.
Sometimes a writer deliberately puts subtext into their work, usually this is in the form of metaphors, where something in the story actually represents something else. If this is not strongly pointed out or even alluded to by the narration or directly discussed by the characters, it's a form of subtext.
However! Subtextual meaning still exists when unintended. For example, you might say that Batman is an implicit endorsement of western authoritarianism and cultural dominance, being a story about a straight cis white American man with lots of money who is stacked with muscles like a classical god and dressed in a costume that is a sort of symbolic nudity, and a cloak (a symbol of rulership) who is celebrated for freely blasting his way around the city in his powerful muscle car hitting people who refuse to conform, often due to mental illness, and is attractive to every woman he meets.
This is almost certainly not intentional subtext. But that doesn't mean that it's an invalid thing for a literary critic to say, or should simply be dismissed. Acknowledging this as a valid way to read batman can tell you a lot about the people who are obsessed with him and how he's remained one of the most popular characters in the world for decades. It might also make you a better writer if you can think in such an objective, abstract way about deliberate versus unintended subtext and how your work could be read.
The entire point of literary study is to understand ourselves, humans, through texts. What we deliberately say about our desires, hopes and fears... and what we might say involuntarily. Was Dracula intended to reflect the fears of strangers from countries we knew little about coming over and destroying the purity of our English women? Or is that an element of unintended subtext? Are classic Disney villains often coded gay in their appearance and affect deliberately to demonise homosexuality, or is it an accident of cinematic tradition based on much older homophobic tropes used unthinkingly, or perhaps a reflection of subconscious fears and biases the creators of those movies might have had?
It's fine to just enjoy something for fun because it's fun. I'm not going to rain on your parade if you like... I dunno... Sword Art Online or something, but if you're studying something in English Literature... well, the whole point is to find things to discuss, and if you can't find anything to discuss about a text, whether the author intended it or not.... you're not looking hard enough.
I think that being able to analyze a piece and find deeper meaning is sort of what sets Literature apart from literature. Standard popcorn novels are not what English teacher tend to pick because they are mostly designed for just enjoyment.
However, I do feel like sometimes people see symbols that the author never intended. I once heard a professor who thought all apples symbolized the fall of man. And all wine symbolized blood.
I think it depends on what you're going for when writing.
Not everyone reads looking for some deep meaning and having their life changed by a book. Some people just want to read as entertainment or escapism.
Having EVERYTHING in a story have some sort of deep meaning to it is a bit elitist but in the case of English teachers, that might be a different situation. For a teacher, I imagine that want the student to be able to critically think about the work. A lot of books that teachers assign in school is for a purpose, like Animal Farm or Dante's Inferno.
Short answer: No I don't think stories need to have any deep meaning to them if that's not what the writer is going for. Different strokes for different folks.
I think one of the major issues with English Lit as a subject that leads to a lot of frustration in students, at least when I was studying it, was that many teachers wouldn't so much have you finding meanings in the text so much as tell you what the meaning is and that is the meaning, the only meaning, definitely what the author intended and all other meanings are wrong. Which, as I'm sure many of us know, not really how it should work. But lots of teachers do teach it like that. For instance, I once went off script and wrote about Macbeth wrote an essay on why it's actually about impotency and the teacher went off because it wasn't what they'd taught us the meaning and symbolism but I was familiar with Macbeth so wrote my own stuff.
I definitely think this sort of teaching when it comes to finding meanings is what gives it a bad name and leads to people getting frustrated with "everything has a meaning" in English teachers. Especially when they also insist this is absolutely what the author meant, and this can lead to new writers thinking every sentence they write has to have a deeper meaning. And especially especially when teachers don't bother explaining how English Lit is different from English Language classes, where they're sometime just all collected together under the umbrella of English class, so it's never made clear there's a difference.
Yikes, those teachers are definitely doing it wrong. The whole point is supposed to be that if your analysis can be supported by citations from the text and logical assertions, that it's a valid analysis.
Of course... you always get bad teachers. Like I had a lecturer on my Tolkien module who simply considered the idea that Tolkien had some racist beliefs, even just ones typical of the time and that he put in without thinking rather than deliberately, to be incorrect, no matter how much you pointed out passages that would reasonably allow a person to conclude that. 
Look how well 50 Shades of Grey did! 
Edit: Whoops didn't see @HGohwell post above. Lol!
While i agree that everything communicates to some degree, it is important to make a distinction from unintentional subtext and the biases of the person interpreting the work.
Sometimes people just try to look for subtext when there isnt anything deeper down there.
A solid example is the hype about the movie Avatar (the one with the blue aliens). Dont get me wrong, i liked that movie, it was entertaining, with solid world building and the visuals were pretty unique. But the plot is basically Pocahontas in space.
In my opinion, I think every single piece of media has some kind of underlying symbolism to it. Yes, even the pulpy junky stuff that people read just for pleasure.
We all have our biases and subtle influences and those are reflected in our work. For example, if we look at the horror genre (specifically the horror genre in the west), it's always been heavily influenced by the culture and context of the time they were made.
Fear of nuclear weapons = giant mutant monster movies
Fear of other cultures/people invading our country = The Thing and Invasion of the Body Snatchers
Fear of pesky teenagers, sex and drugs = slasher movies
Fear of the other humans and illness = zombie movies
It's super interesting in my opinion. Makes me wonder how media is going to be influenced by the subtext of 2020.
Sometimes I will intentionally think of a symbol and employ a motif for deeper meaning, but other times things might just be colored by my subconscious or life experience. So for my works it's usually more unintentional symbolism than intentional. Like on occasion I've had readers comment on certain aspects of my work that make me rethink it and go, "hm, maybe they're right! Guess it was my subconscious working."
Of course things can be read into each line included in a piece, but I don't like it when an analyst insists that the author meant such and such when they didn't. Or the thing in question can symbolize something else entirely. Like a cigar doesn't have to be penile, but it could symbolize looming death. And then again sometimes a cigar is just a cigar.
While I don't go overboard with symbolism myself, I do feel a touch here and there adds to the depth of a story. Not to the point of every sentence dripping with symbolism and subtext, but having major symbols that represent themes in the story.
For example, with my magical-girl stories, while each of the girls' alter egos isn't necessarily symbolic, the protagonists' are, having a deeper meaning pertaining to their role in and growth throughout the story. Papillon also has the main character's selfies of her and her friends' past as a significant symbol.
well it depends if you're shooting for high literature or just something fun. not ever story even needs character development to be good. well scratch that, not every story needs character growth to be good. character development can be defined as just writing a complex character through the course of the story.
but yeah, not everyone has to have meaning
I think you can have both. Even stories that may not appear to have any symbolism may have a lot of symbolism to the author and their understanding of the world. You see this a lot with stories that children write. Stuff that seems random isn't random to them--it relates to things they've observed in their own world.
So in that sense...yes everything could have symbolism if you looked closely enough, because language itself has meaning. Language in itself is a very weird, abstract thing if you think about it too long.
But do I plan things with symbolism? Yes. I like to put symbolism in my work. I think those are my best pieces. But do I think about it all the time? Nah, usually things just kind of fall into place where they need to be, and when I notice that, I will move things around to wink wink nudge nudge to my audience that something symbolic is happening. Story structure tends to lend itself towards being symbolic, especially if you're following a very Hero's Journey type of structure.
When I write I write the story. Then my beta readers tell me they enjoyed the symbolism etc and I have no clue what they're talking about because I didn't put it in there on purpose, it just naturally occurred as I wrote. Needless to say, I don't tell them that.
There is no inherent meaning to a rose, that doesn't mean that the meanings people have ascribed to it and pull away from it have no value. Humans do this with everything, this shouldn't be an issue when they do it to other human creations as well. Perhaps the author didn't intend for a certain message to come through in their work, but if that's the message a significant amount of people found in it, then that's still warrants discussion, I believe.
I've mentioned this in other threads, but I'm one of those nerds who actually enjoys overanalyzing the art I experience, even if it's a conclusion other people would not have gotten out of it. In fact, I'm a comedian and I'm pretty sure this is the foundation for most comedy - you look at something everyone's familiar with from a different perspective and then you point out, "Hey, this is weird right? It wasn't supposed to be weird, but it's weird, don't you think?"
Even outside of my comedic work (which is the only work I've presented publicly, so far) I find this sort of attitude is valuable to my writing. One of the ways to figure out where your story should go is by determining what the overall theme is; sometimes I get stuck on what happens next in my story and I think to myself "Based on everything that's happened so far, what is my story trying to say? If the message is building up to say X, then maybe the next course of events should enforce that message." Now, like I said, I haven't shared these works of mine yet, so I have no way of confirming whether or not this has been to the benefit of my writing, but I at least feel like it has. Or it's at least helped me get through my "1000 words a day" goal.
And on the topic of English class and how it's taught: all the literature you read in that class will have been curated specifically for this type of teaching. Hamlet didn't get assigned to the syllabus out of random chance - it's been studied for centuries by academics, so there's already a consensus that it's a work that's rife with deeper meanings and symbolism. They ask you to analyze these works because there's so much you could pull out of them that it should come relatively easy. Of course, this leads us to the problem of teachers thinking "Your analysis doesn't match what's in the teacher's handbook, so you fail," but that's just a problem with bad teachers and not the field of literary analysis as a whole.
I once read somewhere that every word we say and write has intent to it--there's always a reason why we utter something. With that said, I think it makes sense that the writer would have purpose with every word he wrote. He wants to say something, he wants to tell a story and to do that in a creative way he uses symbolism, foreshadowing, and other literary methods. Why would he write dialogue for the sake of having dialogue? That is why analyzing literature can be so intriguing because reading between the lines can give the reader a glimpse of what the writer is thinking.
In the end, I think every part of the book has a purpose and not just added in for no reason. It can tell what kind of character they are, or what world you are in, it can be commentary, etc.
I think they confuse "trying to sound deep" with writing with purpose. I feel like every story has a point to WHY it's being told. That being said it doesn't have to be a very DEEP point. If you may bare with me, just look at Dragon Ball, the point of that story is a fun fantastical journey with the main character trying to improve themselves.
If you're writing a story you may not be thinking about all those deep symbolism but instead create them by accident. Which could be fun on it's own for the fans to speculate on the importance of so and so scenes when in reality you never intended it.
i.e. The curtain was blue because, the director liked blue curtains.
WHY do I write certain parts? As long as it serves the story, either Character dynamic, development, the plot. I need you to care about my characters and why their doing what their doing. There's a reason I don't show my Character doing the laundry with nothing extraordinary happening. Who would want to read that?
Bottom line to me is, you write something because it's interesting. You got something you want to say that hasn't been said before or hasn't been told the WAY you would. Apologies for the long winded drivel.
I wish you the best and keep writing!
-sincerely
I don't write for the sake of something major in this world, nor do I wish to traverse any subjects and topics on purpose either. I write for the sake of the characters that I created, to tell their story and use their accompanied fictional world to do so.
Fiction is not reality and it is not advised to treat it as such in order to fix something in your everyday life. However, you can use it as a tool to escape from unpleasantries in real life. 
I made some episode using only symbolism, no one understood but me 
was very proud, but it’s quite useless to the world... so I kind of agree with:
I made some episode with 0 intended symbolism or subtext, was less proud, but they were more popular, probably more entertaining too, even for me when making them, but two weeks after even I couldn’t remember them, and I almost never look back.
I think that sums it to me at this point, so I’m trying to find the right balance, a never ending quest really...