Last time I posed the question: why are people so keen to conflate questions of ethics with questions of legality? One possible explanation is that the law offers people a ready-made ethics, backed up by social pressure and convincing punishments, so it's easier to just go along with that than put in the effort to think up an ethics of your own. That explanation is very self-congratulatory, though, so for that reason alone I'm inclined to reject it. What other options are there?
Well, you might say that discussing ethics is pointless, since there's no way institutions are going to respond to ethical accusations. They might respond to legal accusations, though, so discussing legality is useful. However, discussing ethics can help you decide whether you support the way an institution is acting - it won't affect the institution, but it might prevent you from taking unethical actions later (say, joining the army).
You might argue that the law, in general, is ethical - that the existence of the law is morally a good thing, despite the problems with it. To obey the law is to maintain it, since the law in part is sustained through constant obedience, so obeying the law is a good thing. This doesn't seem like a major consideration, though. If we're debating whether to drop bombs on some Middle Eastern dictatorship, is general social attitude towards the law really that important?