I don't know, I don't think there's anything really wrong with using the word as an insult because I don't think it's actually a slur. If anyone can point me to something that shows "troglodyte" in particular is used to refer to any disadvantaged group (like people with DS), I will retract this and never use it again. Like several other comrades who have already commented, I've used troglodyte for years to refer to the same people we all tend to call chuds here. In fact, cannibalistic humanoid underground dweller is pretty damn close to troglodyte. Speaking of which...

If you're going to dehumanize a person, I think it's best to call them something that's entirely unhuman (e.g. demon, ghoul, etc.) rather than something human-like (e.g. orc, ape, etc.)

That's not really the problem, as I see it. There's no line between "unhuman" and "human-like." How is ghoul or demon any different than orc in that respect? Not to be cliche, but it really is all about the context. Orc in general wasn't bad to use per se, but now that it's being used to specifically refer to Russians or more generally, Asians, it has become problematic. Ape is pretty obviously not a good word to use in most cases because of the history of it's use to dehumanize people based on race. But even then, I wouldn't consider it a slur if I were to playfully say to my large, muscular, white friend "you big ape!"

All that said, as always I'm open to being shown where I might be wrong.

If I'm understanding HornyOnMain (OP) correctly, she's not trying to say it shouldn't be used, just that it's odd and suspicious that libs seem to have suddenly picked up on it and are throwing it around incessantly. I fully agree on that.