Leftism was the cause of the worst crimes of the 20th century (whose death tolls wildly exceed even that of WWII). The real tail risk resides in views that are considered perfectly respectable.
Just wait until you see the death tolls of capitalism in general.
That would require the capitalism to end, so I hope we never get to see that. And considering that the only realistic scenario of ending capitalism before any of the people reading this are dead is world takeover by China - you probably hope that too, once you think about it.