If there ever was a side of a war that could be argued for it was "The Allies" in WWII. But the USA didn't join in because of the atrocities. There was a very strong movement in the US that wasn't against war as such but was against "foreign involvement". To paraphase the idea very loosely-- "let the foreign trash kill each other off. We are the USA, strong and pure, and we will survive and thrive without them."

What flipped the switch on that was nothing in Europe--- it was Pearl Harbor. The (non-Caucasian) foreign trash were now trying to kill US, the USA.

As for nobody being pro-war (or willing to admit to being pro-war)-- that's a new thing, since the World Wars, really. Before that the MAJORITY ( or at least the published majority) view was that war was good for both countries and individuals. It got warriors into physical condition and taught courage and endurance. The Boy Scouts were meant to teach the virtues of war to young men. Young WOMEN, called girls. got the Brownie Scout oath: "to help other people at all times, especially those at home".