Well, the media sort of presents it as a freak show, so I'd say the majority of mundanes that aren't Internet savvy and don't know what exactly Otherkin is tend to view it as a curiosity.
I think mostly, mundanes view 'Kin as different, misguided, or downright nuts. I mean, it's the same as being transgendered, in a way; it's a different way of being that others who don't experience it can't understand very well.
(I use the term "mundanes" loosely, mostly because I used to read the Xanth books. :) )
I view Otherkin, and in fact anyone who feels they were born into the wrong body or anything similar, as a valid identity, just because-- well, I don't care if a person I.D.'s as a toaster, everyone has the right to be themselves.