Why is it Fascism to not want to see art of character having sex with their children or something like that?
You're conflating "I don't want to see that" with "Nobody should write/draw that."
You're allowed to have boundaries. You're allowed to ask people to properly tag things. You're allowed to block those tags and those people. You are allowed to leave a space you're uncomfortable in. You are allowed to, and, in fact, encouraged to curate your own internet experience yourself. These are good and healthy behaviors.
The moment you let your personal feelings dictate what you believe other people can and cannot do with fictional characters, even out of your sight, even in the privacy of their own spaces, is the moment you fall into fascist thinking. This is the core of being anti-ship - the idea that because you find certain content distasteful or even triggering, nobody anywhere should be allowed to produce or engage with said content. That is censorship. That is fascism.
I am proship. I have a lot of ship tags blocked/filtered. These things are not antithetical to each other. In the grand scheme of things, I don't actually care that people are creating content for those ships, I just don't want to see it, so I've used to tools at my disposal to curate my own internet experience. They have their sandbox, and I'm happy to let them play in it, but I'm not going to join them. Simple as.
Anti-shippers, on the other hand, see that sandbox and think it's okay to barge over there and tell people they shouldn't be playing in it. They think it's okay to try to have that sandbox removed. "What if the sandbox is dangerous?" If that's what you think, then avoid it. You don't have to play in it. You don't even have to associate with people who play in it. If somebody is trying to force you or trick you or guilt you into playing in that sandbox, then they're in the wrong. If you want to talk about how dangerous you think the sandbox is, that's your right, but be aware that if you approach the sandbox on your own and attempt to sermonize, the people playing there are rightfully gonna get pissed off at you.
Do you understand now? If not, there are more posts about this. I'm answering this on the generous assumption that this is genuine question being asked in good faith, but it will be the last time.
As an addendum: "I don't care about how other people play with fictional characters" does not in any way correlate to "I condone these actions/scenarios happening in real life." That sort of conclusion speaks more to your own thought patterns than anybody else's.