You are just as responsible for your fandom activism as creators are for their fanworks.
More so, in fact, because your primary purpose is telling people what to do or not do. Any instructive value in creative work is understood to be subordinate to entertainment and self-expression, but if you’re out there explicitly advocating for something, you’d damn well be ready to own it. Including all its implications and potential negative effects.
That means: If you’re urging people not to create some kind of fanwork because you think that’ll protect a vulnerable group, you’d better be ready to account for the members of that group who make it, enjoy it, and find solace in it.
That means: If you’re urging retaliation against creators, you are absofuckinglutely responsible for the harm that befalls them as a result, including harm to members of the group you’re trying to protect.
That means: If you’re holding everyone else to high standards about how they could affect someone with a trigger-able mental illness, you need to hold yourself to the same standards, including effects on people whose anxiety manifests as over-scrupulosity or intrusive thoughts.
That means: If you’re shaming erotica you find “gross,” you don’t get to blow off conversations about how that shame plays into conservative sexual-purity enforcement. You don’t get to wash your hands of the implications, whether or not that’s what you meant. Explicit activism has far more duty to consider indirect implications than anyone’s personal pursuit of sexual fulfillment does.
That means: If your activism has garnered you a huge follower count, you are responsible for the exposure you inflict on the people you pick fights with, and the dogpiles or hate mobs you incite. This can be a tough thing to learn if you get popular overnight, and even well-meaning people fumble with it at first, but it’s something you have to figure out. And don’t fucking give me that “it was just a block list, I didn’t mean for anyone to go into their askboxes on anon and tell them all to kill themselves” crap, the only people fooled by it are the ones looking for an excuse to be fooled.
That means: You are responsible for assessing the relative power and influence of the people you’re addressing, and not griefing marginalized subcultural small fry over artistic sins that are far more egregious among canon creators. Especially canon creators who are just as accessible on Twitter as fanwork creators are on Tumblr.
(Pre-emptive response to objections to the preceding paragraph: Only going after people you know you have social power over isn’t activism, it’s bullying with a thin veneer of activist lingo smeared over it. Only trying to clean up your immediate surroundings isn’t activism, it’s complaining to the local homeowners’ association–valid enough if someone’s running their chainsaw at 2am, but if you just can’t stand Betty’s problematic lawn flamingoes, dressing it up as concern for what tacky decorations say about the neighborhood is a little precious.)
If any of that is too burdensome for you, I suggest you take the advice fandom activists tend to have for fanartists and authors: if you can’t do it without doing damage and you’re not prepared to deal with the consequences, abstain. Restrict your activism to shit that’s not going to hurt people, even if that’s just being the best role model you can be.
You want to set yourself up as a moral authority? You want to dictate what people can and can’t create without activist blowback? That’s power–and yes, local power in a community can exist irrespective of society-wide systemic advantage. With power comes responsibility. Use it wisely or not, as you choose, but don’t act like you get to hold anyone accountable for their art’s indirect potential to harm if you don’t want to be accountable for your direct advocacy.