I'm struck by how much the shooter's mindset appears completely detached from those of his friends and loved ones

[EdmondDantes_]

11. Do you mean in the US after the 1970s?

Because if you mean worldwide, the 20th century is littered with many communist military groups. I'll grant you that in the US after the 1960s and 1970s there's been very little left wing gun violence. Not to dispute that in the US there has been far more right wing gun violence. But I wonder if that's because we "won" the culture war on so many issues at least in the eyes of many on the right on abortion, same sex marriage, whatever they think is going on with schools turning kids trans and providing litter box and whatever nutty theories they have, up until recently affirmative action, the civil rights movement, the women's movement, etc. While obviously we have a long way to go on many issues and there's been backsliding on things, it's a lot harder to point to things to cause us to be violent.

FARC, Castro, Che, any of the Soviet leaders, Mao, offshoots of the IRA, etc.

You can find more specifics at the link for various left wing violent groups.

https://en.m.wikipedia.org/wiki/Left-wing_terrorism