I think the best way to stop "oppressive" leftists or any associated violence is by getting back to the basics. The right-wing economic policies which make the rich richer, the poor poorer, and shrink the middle class are what need to be changed. The main problem with the left in recent decades is that they've allowed themselves to become distracted by social issues and have all but abandoned their economic principles. That also needs to change.
By pressing their social agenda, the left has played into the hands of the right, and as a result, they've successfully created divisions among the lower classes - black vs. white, men vs. women, etc. They might be good at raising a ruckus or disrupting college campuses, but they have little to no staying power when it comes to working class Americans. They come from completely different worlds.
It's somewhat ironic, in a way. By violently opposing a ban on Muslims, curtailed immigration, border wall, etc., they're ostensibly trying to appeal to the "bleeding heart" crowd. The implication here is that it's cruel and uncharitable for the richest nation in the world to coldly turn these refugees away. That may make perfect sense to liberals who have homes in The Hamptons, but for the average working stiff struggling to feed his family and keep a roof over their heads, it's not going to make the same impression. It's not that they're not compassionate or sympathetic, but it's often very difficult to worry about those who are far away when there's so much suffering closer to home.