Zing

From my point of view any military intervention that I have seen in my lifestyle has had a payout or some sort of gain for those doing the invading places with no gain are left alone. Sometimes nasty dangerous fundamentalists have even been aided

Pol Pot in Cambodia was guilty of genacide and left at it .He also was indirectly kept strong by the west while Cambodia was occupied by Vietnam

Idi Amin in Uganda
Robert Mugabe in Uganda
all as guilty for crimes against humanity as Saddam Hussein and the ilk

Then look at who the US have helped. We all know the US helped arm Iraq in their war against Iran. Why do you think they did that? did they think Saddam was the better humanitarian? What about the US arming the Mujahideen. Did they do that cuz they thought Mulah Omar was a great leader or was it because they just didnt want Russia to have the land?

There are plenty of places where intervention could save hundreds of thousands and Diplomacy would improves lives but the US ( and the rest of the UN(also Pol Pot had a seat on the UN)) but there is no gain in it for them so they do nothing