Well, I happen to live with one that I consider to be less than human, but that has nothing to do with his hobby. It has everything to do with his terrible hygene (sp? it's been a damn long time since I've even had to mention such a term) awful manners, and general dickishness.
I know not all furries are like that, hell I used to be on a site where some of the smartest and kindest were furries, but I'd be lying if I said the experience of living with the insufferable prick for the better part of the year hadn't left a negative mark.
Back to the topic, I think perhaps such an issue may be far further spread. In this age of promotion of the "perfect human" it's easy for people to consider themselves not that human at all. Hell, I don't act like a human, I certainly don't look much like one is supposed to look, and I very much doubt my thoughts are similiar to my fellow man, so general observational logic would suggest I'm not completely human, or at least, not a normal one.
I guess sometimes one may wish they were not part of the human race, such can be their cruelty. Of course, there are times where one would very much like to be a part of it as well. It's an interesting subject, and it touches upon a lot to the open mind. I mean yes, if one was to consider oneself to be non human, are we to treat such a person? Is there any harm in it, or would the escape from it cause yet more harm? Which leads us to question who we are to dictate exactly what a "sane mind" is, and thus what reality is.
And it is at this point I realise my own ability to take a single train of thought far further than the tracks itself, or rather how far people are willing to read.