Leftist groups are composed of multiple classes of failure, the sociopaths are a small enough group that they usually end up only in management. The shock troops of leftist movements are basically religious zealots, that worship the state or communist ideology instead of god. Leftiist ideologies more closely resemble religions than economic or functional political theories.

Communism in particular is a structure uniquely suited to allowing sociopaths to manipulate large groups of useful idiots. Stalin was almost certainly one. Lenin and hitler were probably more deranged than sociopathic - the high functioning sociopaths usually succeed leadership rather than creating a movement.