If otherkinnery has a place in social justice discussions, then it’s only in so far as religions and other belief systems have place in them. And you’re in luck, lots of liberals/SJ’ers actually care about religious diversity and freedom of religion (just look at how they all flock to defend Islam). So IMHO if you frame your kinnery in terms of a belief system (rather than in terms of personal identity*) then you might have better luck in the SJ circles plus people may view you as more honest/sensible than the average tumblrkin (because you’d be admitting that your experience is subjective and quite possibly has nothing to do with universal truth at all — but regardless of that you have the right to live with your beliefs).
(*Imagine if, say, a Christian phrased their beliefs in terms of identity. Imagine they said they identify as someone who is inherently Christian, that it can’t ever change because it just can’t and he has no choice at all because it’s simply true, and imagine he should be allowed to do all the things his beliefs tell him without criticism because it is supposedly a part of his inherent identity.)
I think it’s really sneaky and bastardly that some otherkin and plurals try to edge their way in as an identity group on par with other oft-mentioned identity groups (you know who I’m talking about), in order to have a slice of that attention and support that they receive. Problem is that you’re not justified in receiving a comparable amount of support/understanding from the wide audience. Of course you want to think that you are, but you’re not. As a group you’re somewhere on par with various new religious movements, like the Raëlians. You deserve about as much special accommodation and outsiders “educating” themselves about your condition as they do.
Now why is that?
Obvious. Because you have no proof and your explanations are outside of this world. If you think your claims of your experiences should be enough then obviously you don’t understand how the real world works. (People [the “wide audience”] should have more important concerns than things that can’t even be verified as legitimate concerns.) Things like reincarnation, spirits or “co-consciousness” (“headmates”), and even species dysphoria (for the “psychological” otherkin) aren’t even coming close to being considered real. They don’t even sound likely.
I personally support reincarnation research and looking further into things like species dysphoria and whatever other things that may explain some people’s claims. Not that I really believe we might get some positive results but it would be closed-minded not to try at all. Everything is possible, after all. Just some things are more likely to be possible than others, and we don’t actually have a shortage of likely explanations for certain otherkin and plural claims.