I find it funny when you talk to Powder Gangers about their thoughts on the NCR they say it's opressive and evil to the point where you must visualize it as being on par with the Nazi's Third Riech. However asking them how they got themselves in jail and they were either stealing from, murdering or blowing up people or the NCR. Then the whole freedom fighters [censored] just dissapears.

Why is it that everyone who activly rebels against the NCR deserved to be treated like criminals? I don't expect Che Guvera, but these guys are just whiney scum. Even the Khans beef with the NCR seems minor when you consider they were attacking not only their military, but their civilians. Then they cry crocodile tears when the NCR respondes in the same brutal manner they would? The Kings were treating NCR citizens badly so the soldiers stepped in.

Is their anyone who rebels against NCR that hasen't instigated a conflict with them?

Think the history of Vault city involves some dark history from them. Can't remember.
House will be targeted by them with time.
Worth noting that they were willing to completely destroy Boulder city for war. Not a living community I don't think, but yeah wtf they blew up a bunch of buildings not in their territory.

Other than that, it's WITHIN the NCR. They don't oppress other nations; they oppress their own kind. And somewhat coincidentally, they insist everyone become a citizen of the NCR.