I feel like fanon fans fundamentally just do not understand why comic fans have such a complaint about the way fanon fans interact and contribute to the fandom. Even those that are comic readers, but prefer or enjoy fanon, hold the mindset that fanon is more akin to "goofy crackfic and whump", which does have its place in fandom as a staple.
The issue is, there is a clear difference between fandom staples (like crack and whump) and what comic fanon has become.
Comic fanon has become a monolith in comic spaces where thousands of people celebrate and encourage illiteracy, where fanon concepts are lauded as facts, where non-readers speak as authority on comics, where many many fanon concepts are rooted in racism, misogyny, ableism, xenophobia and classism, where any character that is not a Bat or Bat-adjacent is maligned and mischaracterized to be a prop for their nearest Bat (Hal is Bruce's punching bag, Bart is Tim and Kon's baby). Even the Bats are flanderized into tropes.
Everyone who likes comics and other characters has to endure at some point someone who has never bothered to get to actually know these comics being told their comics are stupid or their non-Bat character is only good if tied with a Bat.
It gets exhausting after a while, so fics that might be rightfully crack or whump, depending on the content, are met with suspicion because they feed this aggressive fanon machine.
They contribute to a problem, and it's a problem that thousands of people outright refuse is a problem because they benefit from the problem (they like the content even if it's racist).
So I get told to kill myself for correcting fanon myth held as fact (Clark abandoned Kon, no he didn't), even phrased in the most gentle of ways.
Then I get people telling me that Bart is the r-slur and a sweet innocent baby (he's capable and his friends' age, curses all the time and tried to get his mentor laid).
Then I get told I'm ableist for pointing out that the "silent Cass trope" is racist.
Then I see fanon concepts held as FACTS where the Green Lanterns are terrified of Batman, or Barry Allen can't solve a crossword, or Clark Kent (an investigative journalist) can't solve a mystery and they need Batman to help them.
Any opposition to this is frequently met with accusations of hating fun, or gatekeeping, and fanon fans refuse to acknowledge that they are being at least little bit shitty.
Anyway, fanon content creators are free to create whatever they want, but comic fans that don't want to deal with being told their comics are stupid have every right to call out inappropriate behavior. At some point you have to admit maybe there is a problem, and you're contributing to it.
We cannot ignore it, we cannot filter it out, it is relentless.
