While revising five editions of my textbook on abnormal psychology, I have found that drugs and therapy offer disappointingly little additional help for the mentally ill than they did 25 years ago — despite billions of dollars in funding. And there is zero promise that any developments I am aware of will help curb the violence that mentally ill persons commit.
As for progress on restraining or rehabilitating evil people, the past record and future promise are even more dismal. I know of no development that has much reduced recidivism or violence or done more to identify violent offenders in advance than was in place a generation ago.
I conclude from all this that progress in reducing violence through either helping the mentally ill or curbing the impulses of violent, non-crazy people will be very slow in coming, perhaps even fruitless. That is not where the leverage is.
Crazy people and evil people can commit mass murder, and they always do it with guns. Our society’s only real leverage, at least in the near term, lies in reducing access to guns.