I dislike love triangles with a passion, but just the fact of having one doesn't make something bad writing. And there are PLENTY of "bad" books in Adult, New Adult, and Middle Grade. That isn't exclusive to YA and never will be. But how do you define "bad"? Just because one person didn't like something doesn't mean it's bad, it sold for a reason. Average Jane & Joe will read something to be entertained, not to critique every sentence for its literary perfection. Personally, I couldn't stand Ready Player One. There was nothing likeable about any of the characters, the telling style is 100% not for me, yet it sold millions. Same with 50 Shades, the excerpts I read were laughably bad to me and so even if I read erotica I'd have never read the books. Yet it still sold millions. How would I be able to sit here and say it's bad just because I didn't like it? One persons trash is someone elses "best book ever" is someone really going to sit there and tell someone else they can't like this book because they thought the writing was bad?
You need to have an age group for every possible reader because reality is lots of people want to read characters they relate to. From Middle Grade to Adult, there will always be someone who wants to relate to what they read. Can we really ban an entire age group just because someone personally doesn't like it?
Pick an age group and I guarantee you, you can find an example of "bad" writing somewhere be it traditionally published, on Tapas, Wattpad, wherever. Trying to ban an age group just reeks of snobism to me.
I'm a grown woman and I write books that typically span the cusp of being YA or NA mostly because I don't care enough to straddle a firm line either way. I write what I want to write because I want to write it. I'll probably never be published simply because I'll never have the confidence to pursue it, so I have the luxury of not having to conform to any kind of box for sell-ability. But reality is, YA sells well because lots of teens want to read about teens. For the most part they couldn't give two craps about a 30-something having adventures, relationship drama, or whatever else. They want to see versions of themselves doing those things. They want a character who can help them, through fiction, with their own problems. Regardless of if the writing is "good" or "bad" there is nothing wrong with someone wanting to relate to what they read and it should never be banned.