First things first. For a person to shoot children in schools, there are only two possibilities. 1. The person is clinically insane (at which point we will drag him/her to the psychologist) 2. see number 1.
Everything has a risk, like it or not. Okay, so you want a safe and happy environment for everyone using the government? Easy! Just ban everything, control every action, every thought, every second. And.... voila! You have made a 110% safe place for your people!
(small print: such a society is also commonly known as a "prison")