There was also quite a lot of pre-wwII anti-semitism in Europe. It wasn't just Hitler who hated the Jews. Many in the US and England found it useful to minimize the extent of the atrocities being committed by Hitler against the Jews (hell, France marched their Jews off FOR Hitler). They just didn't want to know because claiming ignorance was a better option than claiming moral indecency.

The correlary to today is the large anti-war contingent that is also largely anti-Israel -- like the UN.