There are no rational arguments for my cause if it involves whether I should exist or have rights. I want rights because I want them. How would a rational argument even work?
Once we're there it's an impossible juncture. There's no answer to the sceptic's demand "how do you know?" without some how sharing our subjective experience. Might as well spend your days asking a bat what it means to be a bat.
"people are saying insert group shouldn't exist" is a good-faith and sober characterization of much of that group. Human Bio-Diversity (HBD, i.e. 'scientific' racism) is a very popular topic in the community.
Scott doesn't go there, obviously, but somehow the rhetoric wends it's way there over and over and over and over and over again in the 'community'.
The idea that it's irrelevant and that we needn't know or care what motivates other people when presenting an argument is a pervasive issue with the public conversation. It reduces opportunities for compromise and lessens our chance of learning when we're wrong.
This is a pretty important question, although I don't know how well it applies to specific causes. On the other hand, there are reasonable questions we can ask about rights themselves whose answers are not easily reconcilable. For example:
1. Are rights discovered or invented?
2. If discovered, where do they come from?
3. If invented, can you "uninvent" them?
4. If invented, by what process?
Whereas for you and Mr SSC, the identity is to be studiously ignored in favor of only focusing on the argument, to treat it fairly.
So everyone is using wildly different metrics and then wondering why their interlocutors seem crazy.
Then rights can be rationalized and tweaked a bit so that parties with comparable power do not step on each others' toes, and become allies. This can be seen, more roughly, as "discovery".
Rarely rights are granted by the more powerful to a less powerful because of moral / religious reasons. E.g. the anti-slavery movement in the US had a significant religious component, based on the idea that God created people equal.
More often a more powerful party gives a less powerful party some rights because they need an ally and want to prevent a full-on power struggle. I think women's suffrage had a significant component of this in many places.
Powerful and oppressive parties can definitely "uninvent" rights; look at any totalitarian regime for examples. Say, communist regimes often revoke the right to freely trade. Most oppressive regimes gladly uninvent the right to congregate, and usually the right to free speech. They tend to frame these activities as harmful and unnatural. Regaining them usually involves a power struggle; see above.