You'd think the idea that powerful nations ought to intervene to stop genocides would be a no-brainer. Of course, there's the problem that the sons (and daughters) of powerful nations need not necessarily pay with life or limb to clean up the worst messes humanity makes. That's a legitimate point. And you'd be sure to spot the danger that deciding where to intervene will always be subordinate to the politics of the matter. And of course, inevitably the malicious fools will demand intervention to stop Israel's genocide of the rapidly multiplying Palestinians.
Having said all that, however, I stand by my first statement, that stoping genocide is the right thing to do, even if it has been done only very rarely. My understanding is that it was even agreed upon at the United Nations back in the 1950s, when there was still some hope the United Nations might prove worth its electricity bills.
Apparently I was wrong. The UN is still haggling about the idea, and seems of a mind to drop it. If I follow the argument, it is that the likely candidates to stop genocide are the powerful, rich nations, while the genocidaires are often in poor, undevelped countries, and powerful-rich-vs-poor-undeveloped, poor and undeveloped always have the moral high ground. Or some such argument. Noam Chomsky is at the forefront of the people who'd prefer mass death to American actions to save lives.
Just for the record, by the way: one of the few cases I can think of where outside powers intervened to stop a genocide was in Cambodia. The Vietnamese invaded and stopped the slaughter, backed by the Chinese; most of the rest of the world condemned them for doing so. International politics can be a very strange place.