I'm gonna say probably confirmation bias.
In certain areas of the net there are indeed a lot of 'alt-right' people with anime avatars who make a lot of noise in comment secitons. On the other hand there are also plenty of areas where people seem generally more progressive (e.g. Reddit).
If you hang around at either of those areas a lot you might start to think that everyone in the 'fandom' (for lack of a better term) is like that.