"right" is a problematic term in this case
"done right" is a sufficiently neutral expression often used in engineering context, I don't read moral overtones here.
[effective] repression doesn't cause rebellions
That's just a tautology.
it's mostly because the dead don't complain
Not necessarily "mostly", but historically it has been a very popular way for a "successful" repression. It's a bit more difficult to pull off nowadays, though.
it's not very effective
It depends on who you are repressing -- e.g. if it's an (ethnic, religious, cultural) minority, killing them all is very effective.
Because traditionally you kill the males and enslave the women, you can empirically find defeated populations in the genetic code of the descendants of the winners: they would have some matrilinear admixture, but none (or almost none) of the patrilinear admixture of the losers.
you can empirically find defeated populations in the genetic code of the descendants of the winners
You lost me there. Why is that relevant?
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