I can concede your point partially, that in addition to leftists who commit atrocities, there are leftists who merely enable the mass murderers to gain power, naive of their intentions. There were those in the Kerensky faction that were overjoyed that now that the Communists were in power, they would now be able to abolish capital punishment in the new Soviet Union!
However, you seem to have forgotten about China, Cambodia, North Korea, Cuba, the African Marxist regimes, East Germany, Vietnam, basically the majority of leftist regimes that were murderous nightmares.
Why are you afraid to call them Communists. That is what Joe Stalin. Khrushchev, Brezhnev, Mao, Hoenacher, Ulbricht,
Pol Pot, Kim Il Sung, Ho Chi Minh and Fidel Castro referred to them selves as. They were Communists. To equate the USSR, the PRC, or North Korea, with the left leaning countries of Scandinavia, and sometimes, France, Italy, Spain and Greece is ludicrous. Where are the gulags in Norway, How many millions did the leftist in Sweden kill. How many Danes went to re-education camps never to be heard of again. Everyone that is a Communist is a leftist. Not every leftist is a Communist. To use the term that loosely is no smarter than the leftists referring to anyone with a right slant on politics as a Nazi or a Fascist. There is a difference.