The real reason liberals were opposed to Vietnam is because they didn’t want us fighting a communist army.
That is true, but on the campus front, where I was from 65 to 68 the number of healthy males who were just absolutely terrified of being anywhere near combat was amazing. That is what filled the ranks of many of the ‘anti-war’ demonstrations. A mass of physical cowards. That was the first indication I had that a lot of my fellow Americans were weak weasels and trouble of the sort we now have was inevitable.
Before the beginning of Operation Barbarossa, they didn't want the US to aid England against Germany because the Germans were allied with the Soviet Union.