Ah, lol, I feel like I'm not expressing well what I mean
So, let me try again: If I felt that any of my stories were popular enough to make anybody write fanfictions about it, then I'd add a question to my FAQ where I would explain that I'm alright with anybody writing any fanfiction they want about my stories but that I don't encourage erasing the representation of minority groups *insert the explanation there*. (And I'd probably think long and hard about how to phrase that question and the accompanying answer to make sure no side will feel hurt afterward.)
I wouldn't go and tell that to any fanfiction writer who didn't reach out to me or even actively seek anybody out to say that stuff. Neither do I expect that everyone who reads that note will actually do what I'd like. I'm pretty sure that lots of people won't even care. It's actually alright for me if they decide that they still want to touch that representation since it's not an "I won't allow them to write it", but more of an "I don't really like it but you do you. I just want to make my stance clear because it's something I'm passionate about".
So, mostly in regard to this I guess:
That's really not what I mean. I don't want to denounce any kind of fanfiction anybody would write. I just don't condone erasure and want people to know that and especially why. (Like, look at Riverdale and that's not even fanfiction but an official adaptation.)
I just want people to know what that type of thing can mean (and I do not mean that in an 'they changed that cishet character into a gay guy' or whatever like what @gempompadour originally wrote) to a community that doesn't get much representation anyway and then gets one of the few characters they have taken away from them.
I don't know if I'm making myself clear enough or not I think this is actually less about fanfiction itself and more an 'I owe that to myself and the community'.