If you want to make a significant dent in the mass shooting problem (by the way, the FBI's crime stats page [0] is illuminating on many subjects, not the least of which is that violent crime rates are way down from earlier in the 2000s [1]), you need to start looking at why someone feels shooting up a bunch of innocent people is a valid response to whatever stressor they're feeling. Maybe there is an income inequality, and that can cause someone to feel angry. But there's a leap that needs to be made from "angry" to "mass murderer", and it'd be helpful to understand why that is. I suspect it's mental.

[0] https://ucr.fbi.gov/crime-in-the-u.s/2018/crime-in-the-u.s.-...

[1] https://ucr.fbi.gov/crime-in-the-u.s/2018/crime-in-the-u.s.-...