You're right - the United States isn't obligated to clean up every international mess, and other nations are capable of intervening in conflicts on humanitarian grounds. Which raises (but does not beg) the question, when are such interventions merited? In any violent conflict, the losing side will welcome outside intervention, but that means intervening always involves taking sides. Then it becomes partisan, and not humanitarian.

The perception that supposedly "humanitarian" military action is actually self-interested will be reduced when many nations, having a variety of interests, join together to do something about a conflict. If the U.S. had been able to put together a true coalition for the invasion and occupation of Iraq, it would be a lot harder to say it was all about the oil and the enrichment of Haliburton.