Both far left and far right regimes have resulted in chaos, murder, and repression.

If you're skeptical that leftism can cause violence, the wikipedia list of recent far-left terrorism groups may convince you otherwise: https://en.m.wikipedia.org/wiki/Left-wing_terrorism

And of course, there's the more classical examples: Maoist struggle sessions, the Red Terror, the Cambodian Killing Fields.

Extremism is dangerous. And it's concerning to me that this has become a debatable point.