Is an unflinching commitment to always be anything morally desirable? This suggests that nothing at all could move one to take a different view, and that sort of absolutism might well be felt undesirable. We normally think that it is preferable to take each situation as it comes and then assess how one ought to act. If someone were to say that there were absolutely no circumstances in which violence would be acceptable, it would be difficult to know how to talk to him or her, since there are circumstances in which violence just does seem appropriate.
I suppose another way you could try to get everyone to believe the same thing is coercion, terror, and force, either outright or threatened. Doesn't sound appealing.
So maybe we should rethink what's needed for world peace. Instead of thinking that it requires universal agreement, perhaps we should explore the possibility that it requires only respect for reasonable differences of opinion; instead of everyone's having the same beliefs, we need to work out a way in which sharp differences needn't lead to conflict. (You might reflect on our own society, in the U.S., which is domestically at peace and yet whose citizens have sharply conflicting beliefs about matters of great importance to them.) In this connection, you might be interested in reading Immanuel Kant's Perpetual Peace (1795) or John Rawls' The Law of Peoples (1999).
I'm not sure those who hold that is is just to kill or execute people under certain circumstances believe this simply because "our peers say it is". That might explain why some people have formed this judgment, but it doesn't tell us why we ought to form the judgment, that is, tell us what's to be said in the judgment's defense. (See Question 367 for more on why this would be a problematic argument.) If you think it's wrong, it's worth trying to say why it's wrong. To begin with, you might try to get a sense of the contours of your moral judgments? For instance, do you think we're also "bereft of compassion" to deprive individuals of their freedom? For the remainder of their lives? For five years? Perhaps you'd be interested in Debating the Death Penalty, a collection of essays arguing both sides of the case.
There surely are intelligent and morally thoughtful individuals who are pacifists and believe that going to war is always morally unjustified, However, I think that this view is ultimately morally unacceptable. I believe that there can be circumstances where going to war would be morally justified, for example, cases of collective self-defense. If one political community is unjustly attacked by another, people can be morally justified in defending themselves against attack by going to war against their attacker. This needn't mean that going to war whenever one is attacked would be morally justified. There may be cases where the moral costs of self-defense are too high and, thus, would not be justified. But this doesn't count against there being at least some cases of going to war in self-defense being morally justified.