If you go far enough you wouldn’t be able tell a far leftist from a far right winger. Because they are the same person. There’s no “classic left” about it.
There has been genocides in the past from both sides. One indicator that a faction is going unhinged is that they become authoritarian. They start seeing in black and white and loose their humanity. This can be observed in both left and right. The massacres from the left are brought up all the time, so I’ll bring one up by the right to make it balanced. Don’t forget that the US dropped 2 nuclear bombs on civilians.