It's the moral purism vs. harm reduction conflict. A moral purist will not accept any compromises because they value their personal moral values over everything else, while someone holding harm reduction stances will accept compromises (the lesser evil) even if it morally stains them, to get better actual results. This means a moral purist is okay with letting the greater evil win as long as their own moral purity stays intact

(and the paradox of moral purism is that they in reality go against their own ideals, by letting the greater evil win)