A couple of thoughts:
1. We had access to guns in this country for centuries. We had access to semiautomatic guns for decades. It is not some new technology. These types of shootings are a relatively "new" thing. Columbine was within the past 25 years and that seems to be kind of a marker in time for when this stuff kicked in. So what went wrong around that time?
2. I am young Gen X, for those who are older than me, how were fist fights viewed in your day? I can remember getting in a few scuffles in elementary school in the 80's. By the time middle school rolled around (early 90's) we were starting to hit the zero tolerance type of approach. Fights were an out of school suspension. Period.
3. Quite a bit of the past 25 to 30 years has had quite a bit of focus on the mental health and encouragement of girls. We have really shuffled boys off the stage.
I have my thoughts on a few things I think contribute to this. Degradation of families, moral breakdown of society, the internet, lack of a pressure release valve for boys, poor mental health resources (true mental health issues), the breakdown of our civic unity, a catch and release approach to crime that is not deemed serious enough.....
And when it comes to the guns, it is as simple as this. The heavily armed people in this country do not trust the altruism of the gun grabbers. It's that simple. You want to address the gun issue, you need to start there.