There were a number of socialists who at first supported the Nazis. Not all, but some. There were an even greater number of leftists who idolized Stalin. Today these people get choked up over "McCarthyism" but they just shrug at Stalin's show trials.
Liberals don't care about Stalin or Pol Pot. The NYT was all upset last week because someone critised Mao. According to the NYT if Mao killed 20-50 million; it was OK because China got land reform.
In fact, a lot of them go and visist Castro and say how he's a beloved figure because he gave everyone health care.