I could be wrong, but I don't think there are many posts asserting that the Orc-dispatching RPGers are tacitly approving of colonialism.
What seems to me to generate disagreement is telling those RPGers that the fiction they are creating, the tropes they are deploying, etc, are connected to colonialism, or trade on colonialist or racist ideas.
I can't remember, but I think it's quite liley that somewhere back in the 1980s I used the "Tribesmen" entry from the AD&D Monster Manual (or maybe I'm remembering the "Natives" from X1 The Isle of Dread). I mean, I'd watched black-and-white Tarzan movies and I knew what role "Tribesmen" and "Natives" play in adventure fiction. I don't think I was expressing any attitude towards colonialism, tacit or otherwise.
I wouldn't, now, deploy those sorts of derogatory tropes in my own FRPGing.
When JRRT wanted to convey savage, brutal, largely nameless, evil, what imagery did he reach for? Dark complexion ("swarthy"). "Bandy" (ie horse-riding) legs. Scimitars. Etc. The ready availability of these tropes is not mere coincidence. There's an explanation for it.
How one then responds to that explanation is a further matter, of course.