Hm, well I think this is an interesting topic. While I know the taboo with it, I don't think that as a whole it should be hated so much. Who hasn't known a kid to dress up like an animal at Halloween? I think the problem is when it is sexual. And again, as someone mentioned, that they want to be the animal or the person and that disturbs some people.
Then again, why is pretending to be someone you aren't so terrible? L.A.R.P.ers, while usually teased, are not so ostracized as the fursuiters. Maybe it's in the way they present themselves? Oh well, anyway on topic...
Taking it as just wearing a costume a full body outfit isn't all that weird really. I see it as an art form, sure, a lot of time and work can go into making a good costume. Homemade costumes, especially one made well and that look like who or whatever they are emulating, can be a testimony to someones true devotion to the art or their fanatic devotion to the series they base it off of.
I think the problem with the... Anime Kigurumi is it? Is the 'creepy factor' of the masks. But really, how can fans of any sort of anime complain? The proportions don't translate well into real life. Of course the fans of the anime kigurumi like it, but for those who don't, I think it is just their mind not liking the transfer between the anime and real life.
Again, just my opinion. I personally like more cosplay-still-human-face. Oh if only I had the money for some catears and a tail. Another boring Halloween for me. *sigh*