Politics often makes for strange bedfellows
Was Truman wrong to shake hands with Stalin, perhaps the biggest mass murderer of all time? How about the photo on this page showing Churchill, Roosevelt, and Stalin sharing a laugh?
No. As evil as Stalin was, defeating Hitler was even more important. We couldn't have beat Hitler without Stalin. As the staunch anticommunist Churchill said when Hitler invaded the Soviet Union in 1941,
As for Iraq in the early 1980s, stopping Iran and the spread of the Islamic Revolution was seen as more important than Saddam. At the time, it was probably the right decision.