No, I don't have a boiled down answer. When I try to think about it, rational/right includes not just the outcome of the current engagement, but the incentives and lessons left behind for the next incident.

Okay, here's one example I've used before: torture. It's somewhat orthogonal to the question of following orders, but it bears on the issue of setting up incentives for how often breaking the rules is acceptable. I think the law and the practice should be that torture is illegal and punished strictly. If some person is convinced that imminent harm will result if information isn't extracted from a suspect, and that it's worth going to jail for a long time in order to prevent the harm, then they are able to (which is not the same as authorized) torture. But it's always at the cost of personal sacrifice. So, if you think a million people will die from a nuke, and you're convinced you can actually get information out of someone by immoral and prohibited means (which I think is usually the weakest link in the chain) and you're willing to give up your life or your liberty in order to prevent it, then go for it.

But don't ever expect a hero's welcome for your sacrifice. It's a bad choice that's (conceivably) sometimes necessary. The idea that any moral society would authorize the use of torture in routine situations makes me sick.