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).
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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.