RE: The problem of moral exclusion and dehumanization
I think we have to approach dehumanization from at least a couple different perspectives. Here's what I mean:
At the end of the day, to be "human" is to have an ego. And yet, if science and contemplatives are to be believed, ego is an illusion. And, we'd actually be healthier if we transcended our identity with ego in favor of ...well...that depends on who you ask.
But, in any event, if ego is an illusion, then being "human" is an illusion. And if transcending ego in healthy ways is beneficial, then dehumanization (or de-egoization) is beneficial.
In a sense, our goal should be to help everyone dehumanize themselves--to dehumanize everyone, including ourselves. So, I have no problem with dehumanization per se, but I do have a problem when it is used by one ego (or group of egos) as a way of acheiving a false sense of superiority over another (or a group of others).
None of this applies if you don't define humanity by the presence of ego.
Also "dehumanize" has a negative connotation, taking away humanity. A person who moves past their own ego is better said to be transcending humanity. That may sound like an academic difference, but the former implies being taken, while the latter implies beinf given up by choice.
How else could you define humanity except by the presence of ego? I don't think it's possible. Ego=human.
OP gave a different definition of humanity, and talked about how there are many attempts to define it...
Even then I think you're conflating multiple definitions of ego. Ego can be termed self-awareness for the purposes of defining humanity, however when "contemplatives" talk about Ego...
Well, it can get complicated. I was hoping to find an Eckhart Tolle quote about it but instead there's tons and tons of pages where he talks about it. Apparently a difficult thing to nail down for contemplatives, but this last line sheds some insight for our purposes:
That is to say the self-awareness is separate from the actual Ego, and when these philosophers say to transcend Ego they are talking about something different than the self-awareness you're defining humanity by.