Leftism cannot tolerate opposition. It will always resort to killing dozens, hundreds, thousands, tens-of-thousands, hundreds-of-thousands, millions, tens-of-millions, or more, if it possesses the power to do so, and believes it necessary to advance the cause of Leftism.
Humanity can never afford to forget this fact if humanity hopes to avoid repeat history. Understanding lessons from the last century are vital to the survival of Western civilization.