I feel that it's only appropriate for the LGBT+ community to define itself, and not for others to try to latch on to a marginalized group because "hey, we feel marginalized and want to be connected to this unrelated thing that has attention so that we'll get attention." Sure you could say that people attracted to fictional characters are sexually marginalized, but whether or not it's LGBT+...I'm a little skeptical. Although: I'm pretty sure I remember there being a name for attraction to fictional characters in the ASPEC community.
I can see the connection you're talking about with the anime community and it is kind of scary to think about, but thankfully I've never dealt with too many of that sort personally. On top of that, it's kind of hard for white supremacists (who are typically associated with the alt-right) to get into anime in the first place considering they'd have to like something made by people who are decidedly not white, so that's a plus.
All in all, you can try to call yourself LGBT+ or whatever for liking fictional characters, but if you're already dealing with THOSE PEOPLE(tm) then they're probably just going to make fun of you for it rather than think about themselves in a new light.