Because they didn't? Because cis is a relevant qualifier when discussing the lens of trans marginalisation in greater society? It was a hypothetical in the first place. Again, "die, trans scum" by your logic would make "trans" the insult. It's not. The insult is saying you should die (and "scum"). But I keep repeating this.Then why add any reference at all to the person's gender-identification category? The person is also brown-eyed (say). Why not say "Die, brown-eyed-person scum"?
Evie made a good point about "othering", but at the same time reinforces what I'm trying to say - that anything slots in the "othering" part of the phrase. The anything isn't the insult. At the risk of sounding like a broken record, "die scum" is. But again, we're going in circles. Your argument isn't getting any stronger. You're still defaulting to cis-therefore-scum to the exclusion of all else (as a part of a greater argument that revolves around trying to make "cis" sound like an insult, which has amusing connotations for "trans" that haven't really been thought through. We don't live in a utopia. We are not past labels. We can dream of being past labels, but they are still required, and can be value neutral despite being used offensively at times).
There's nothing dubious about "cis". I mean, Gori disagrees on the linguistic ground of it being lazy / cheap (or words to that effect - sorry @Gori the Grey, I'm not digging for the post at the mo). But "dubious" is a whole other thing.It would also be nice if you stopped othering large swathes of population bluntly with dubious words and then making alarmed faces when said population resists your labelling and insinuations. Counterproductive.
Cis people overwhelmingly other trans people. sophie and other posters have described this, time and time again. You trying to say "but I feel targeted by association". Unlearn that association. Feeling targeted is counterproductive, and leans into the whole "I'll only support you if you're nice to me" instead of what should be the default "I support you because it's the right thing to do regardless of how allegedly mean any one individual is to me".