We didn't hate them until we thought they might actually take us over as well. We weren't fighting Nazis, we were fighting "un-Americans". It's literally just another flavor of racism(that we helped teach the Germans lmao - they loved our concept of eugenics)
Notice how after Nazis it went to Commies, the other "un-American" type.
Kind of hard to talk people going to another war across the sea so soon after WW1. Plus, the US was more divided on WW2 then people tend to think prior to Pearl Harber.