That Socialism and Communism jointly are responsible for over 100 million ruined lives in the 20th century... doesn't seem to "resonate" with the radical Left. The utter failure of their Social Experiment is plain to all except elite American and European liberal intellectuals.
Speak to any imigrant from China/Russia/Vietnam/Cuba/Korea/etc... and they will remind you that Socialist Utopia is a living hell, with the most basic needs like bread and toilet paper nearly impossible to acquire.
A good read: The Politics of Bad Faith by David Horowitz. He reveals how the American Left simply ignores recent history (sort of like the stubborn Clinton supporters we know and love).