Militant: combative and aggressive in support of a political or social cause, and typically favoring extreme, violent, or confrontational methods.

This is accurate and not a negative thing to say. Ukraine has had people the world over join them in this fight. The people who joined the cause are not Ukrainian military members. They are classified as militants.

This doesn't make them bad. Nor is it a negative term. You're the one who's dumping the association onto the word.

Also yes. Russians defending against nazis would have been militants if they are not military members themselves.

It's just a thing about language dude. You're the one attaching the negative association to it.