Working in customer service or help lines for entertainment companies, you will always see these folks. And I have never seen a single complaint pass me by be simply to inform their displeasure or give a critique.
Instead, all of them were demanding for creative changes or for some compensation of product or money due to a taken slight, when it wasn't a legitimate and fair design issue to improve on. Even funnier was we had a regular group of people, about 4-7 people who would pop in every other week or month looking to demand something.
It bears stating there's a vicarious thrill in control, and it's made very dangerous when you consider the internet does help amplify that signal especially when it's couched in "doing it for the greater good" and broadcast to others (often through multiple puppet accounts and bots to make the group and the concern bigger than it really is) and the media that what you're doing is wrong and unwholesome. It doesn't matter what name they're now given, the current groups deserve the same title as the stuffy snobs looking to put an end to comics as an art form and broadcast cartoons: Busybodies.
Seeing the complaints for that Iron Man cover and what to change are almost word for word on the standards presented in the Comic Code Authority that came about from the congressional hearings over the now heavily disproven and very fudged research in "Seduction of the Innocent" by Dr. Fredrick Wertham. It bears noting that Wertham wasn't some cartoon villain out to rid the world of fun and did believe in helping kids, it's just that he believed this art form read by almost every kid in the country harmed them, even if the data he compiled suggested otherwise. Belief, to some of these people, trump fact and, in the process, artistic freedom.
Last year, there was a webcomic that was cancelled a mere few pages in because the design team were two women from New Zealand, and the story took place in Japan, revolving around Japanese voice actors in anime and visual novels and that horrifying injustice would not stand. And it doesn't help matters because it creates a very real chilling effect that emboldens the bullies and the justicars.
To illustrate this isn't a new thing, just something done in a new format, here's a fantastic interview by Rod Serling, creator of the Twilight Zone, done in 1959 talking about how this was done in this time while he was championing smart genre television and adaptations of some of the best sci-fi novelists work and how these demands impeded creativity and prevented the exploration of hot button topics of the day under their current name of "Pre-Censorship". There's some scary parallels with current Youtube issues here. He also made an episode of Twilight Zone revolving around one of these busybodies who went out of their way to get people they didn't agree with fired and their work pulled called "Four O'Clock".
It's one thing to deal with honest, fair critique and being welcoming to fan dialog. I always thank people for reading and enjoying my work when they tell me about how much they liked it. I love it when they ask me questions or behind the scenes stuff on how it turned out that way or whatever. But when someone comes out with wild hyperbole and a very hostile attitude, you either ignore the person, laugh it off, or engage the bully in the most visible public forum you can. Once it becomes clear they're looking to bully you, don't be nice or give benefit of the doubt. Just redefine the debate on your terms, don't respond to questions that make you accept their framework. Make it clear to everyone else who the real villain is. They are not your customer and they are not your fan. Respect is a two way street.