It comes from the Lord of the Rings, that’s just someone using it.

Obfuscatory. The reason people rallied around that specific term can clearly be traced back to Azovites using it.

I don’t think it has anything specifically to do with Muslims.

With the Azovites, it certainly did. Obviously most Russians are not Muslim (nor are they Chechen), so Reddit's reinterpretation of the term is not identical.

It mostly spread as use for Russian soldiers that were just rampaging around

People tend not to qualify it as "just for soldiers" except when doing apologetics

comparing your enemies to characters in a fantasy novel isn’t exactly the worst slur in the world.

I've seen them called Death Eaters and, aside from "read another book" and some other ancillary issues, I think your statement applies well to giving the Russian military such a label.

That's because the Death Eaters are an organization, not a race. You opt-in to being a Death Eater, you can't opt-in or -out of being an orc. Flattening it to "comparing them to characters" is completely flattening the issue of racism.

Of course, the Azovites are viciously racist and Redditors are no stranger to basically every type of xenophobia imaginable, so I think the burden of proof here would be on you to demonstrate that this is an exception to the general trend of racism both Reddit and the Ukrainian military/paramilitary, who can only be dissuaded through great effort from dropping even a fragment of their Nazi iconography.

Edit: I should say that I'm speaking in terms of epistemology and counterargument. I'd much rather you just acknowledge the obvious truth and move on rather than try further to contort the evidence to make Redditors not racist. Some arguments are fun, but this one is tedious.