Creating a society where people actually give a shit about each other would help. So free healthcare, housing and education.

Then theres the disgusting habit our society has of ignoring signs of psychopathy and our how we currently reward bullying. A lot of these shooters were violent bullies before grabbing a gun, and nothing ever gets done about that.

Rewarding kindness needs to start being a thing too. We all need to live together so encouraging a hostile and competitive environment is fucking stupid and needs to stop.