Ok, I have had my moments of wondering if we have some similarities to Weimar Germany, as well.
I had a friend's Croatian mom try to get me to run guns during the Yugoslavian civil war, trust me I am pretty cognizant of the long-standing hatreds there. Sometimes the American general lack of a sense of history is a plus.
Also from the 60s-70s: massive race riots that left cities in flames, hijackings galore, Black Panthers marching with guns in Sacramento leading to Reagan starting the end of open carry as a legal thing, the KKK gunning down protestors in Greensboro, NC in broad daylight with near impunity, the regular use of the National Guard to suppress demonstrations on college campuses (Kent State ring a bell?)....I could keep this up all day.
All the incidents you mention are lone actors. I get nervous about true mass movements getting together to commit violence far more than "firecrackers".