Part of that, particularly from Trump and his supporters, and probably from Antifa and similar groups, is excessive tribalism. They hate the other side and are eager to hurt them. Trump supporters are certainly quite open about that. Antifa might actually be different. It's also possible they actually believe that violence is necessary in order to stop fascism. But any support they may get from the left is probably pure tribalism again.
Of course there's also another aspect to violence from the right: things like lynchings in the 1950s, harassment of women, violence against Muslims and other minorities. Those stem from pure bigotry and a belief in (usually) white male superiority and a right to punish others if they seem too uppity or seem like a threat. I assume most people on the right abhor this, and yet some of these still happen.
This "right to punish others" should be a big red flag, be it from extremists on the right or the left. Both extremes have poor records, historically speaking.
Most importantly, USA is not 19 century Russia in pretty much any way. You went completely offtopic and also conflated antifa with social programs - in discussion about tribalism and biases. Achievement.