Eagle Squadron: The Sanguinary Enforcers of the Liberty Ethic often play this role for various libertist movements in one part of the Associated Worlds or another, strictly freelance, of course, as do some related groups for more specific issues (AI freedom, for example).  They are relatively picky about who they support (given the number of times people want to overthrow the oppressors in order to become just as bad, oppression-wise), but still, it happens enough.

It’s still disappointing an annoying amount of the time.