(1) The False Equivalency of Representation
Even if a fanfic has hundreds of thousands of views and thousands of kudos, it is never going to achieve the same level of cultural impact as big-budget mainstream media. No matter how much wholesome fic you write about Finn, it is not going to be the same as John Boyega’s face on every movie screen everywhere in the world.
(2) The False Equivalency of “They’re Just Fictional Characters”
Because “positive representation” isn’t really a valid concern with fanwork (although, in a collective sense, it absolutely can be, but that’s a different conversation), it doesn’t matter whether your fic or art is about Naruto kissing Sakura or Naruto kissing Sasuke. In fact, those three names are probably nothing more than nonsense words to 99.999% of people on this earth. It also doesn’t matter if you, as some rando on the internet, get off (for whatever reason) on the idea of Sasuke forcing himself on Naruto, Sakura, or both at the same time. They’re just fictional characters, and it does not matter to the broader culture. What does matter is if systematic structures of inequality and discrimination are uncritically reproduced in the fictional texts embraced by fandom without commentary. It’s therefore a false equivalency to put “I don’t like this m/m ship” on the same level of critique as “I don’t like how the source text marginalizes female characters.”
(3) The False Equivalency of GO OUTSIDE
Saying “I don’t like a particular m/m ship” is not only fine, it’s par for the course in fandom. Saying “I don’t like how the source text marginalizes female characters” is also fine, and we could probably use more of that sort of thing in fandom, to be honest. Someone writing about the details of their disappointment regarding a work of fiction is also fine. It’s okay to not like things! What is not okay is sending death and rape threats, accusing people of pedophilia, finding someone’s personal information and threatening to contact their family or employer, and doing things like creating a [username]gokillyourself account on AO3 in order to leave comments containing concrete instructions on how to commit suicide. It is a very clear false equivalency to suggest that expressing a negative opinion about a fictional character is “just as bad” as harassing an actual human being.