I don't see why it wouldn't just be an extension of gender/sex being a protected class.
Could you please elaborate? I still dont understand how anyone could have this viewpoint but its been presented to me as a given without need of any explanation. Like how can a human say they arent a human and be taken seriously?
Well, now you're asking a separate question. Whether or not they should be taken seriously by society is an entirely different manner than whether or not they should be entitled to certain legal protections.
For example, if tomorrow I started a religion that proclaimed Tom Sellick and Kirsten Dunst to be the creators of the universe - most people would rightfully mock me for holding such an absurd belief. But that wouldn't changed the fact that firing me for holding those beliefs would be a violation of my first amendment rights.
If you want to debate the merits of that religious belief, or in your example, whether or not someone's belief that they are an otherkin, then that's a different debate.
You need to establish that otherkin belief is somehow fundamentally different from other gender identity (including that of people like you and me, whose biologicals sex matches their gender identity) in order to argue that they would not be entitled to the same protections that make it illegal to fire someone for being gay, a woman, or a Pagan. "I think it's weird" does not suffice.
There are explicit legal protections for religion, so for the comparison to work, the argument would have to be that otherkin is a form of religious expression.
The question seems to be about the legal basis for hypothetical decisions.
One wrinkle would be the fourteenth amendment, with the idea that protections granted in one area should be accepted elsewhere, although you would still need some local legislature to provide employment protection or whatever to otherkin.
