"Mangeons les riches" -Jean-Jacques Rousseau

More comprehensively perhaps here: https://en.wikipedia.org/wiki/Mass_killings_under_communist_regimes

Of course if you define "leftist" as meaning "doesn't support genocide" amongst other things then obviously leftists don't support genocide. But that doesn't seem to be the actual real world definition.

edit Oh and of course there's Hamas. Left is unabashedly supporting the genocide of Israelis.