People who do bad things don't necessarily do *all the bad things* *all the time*. Depending on the fic, Rumlow's either depicted as an actual trash party rapist or "just" someone who is still loyal to his employer even though he knows they keep themselves a prisoner to use as a human weapon and are planning genocide for their so called greater good.

In any case, nobody argues that he's very much the bad buy. But does that mean he can't feel genuinely sympathetic to the WS once in a while? Or disagree with other people's treatment of him? I don't think so.

Bad people sometimes do nice things. Sometimes even to their victims. That does not make them less evil, only harder to spot.

Sure, sometimes it's nice to have an antagonist who is just plain evil, but I don't think that's the only right way for the bad guys to be written.