While I too abhor war . . . and while I am not saying we should get involved . . .since you asked for comment, I will use the same example you began with: Hitler before WWII.
Here I become seriously conflicted. Would earlier involvement have avoided the Holocaus and prevented the death of about 9 million, would it have stopped Soviet expansion, would it have changed history so that Israel never became a state again in modern times?
Of course we'll never know. But we do know that war seems to just be something humanity just can't seem to live without. Where did that damn gene come from?
To say it another way, when does it become in our national interest to become involved . . . when does it become necessary to be that policeman . . . under what circumstances . . . never?
I don't know the answers, and those questions above are not the only ones, but I think they are worth considering.
Barry