re: Mass shootings would stop immediately if we did a few simple things

I don't think policies, rules, guidelines, mandates, laws etc. will or can change the fundamental human nature that deals with issue of the human heart, choices to love, the need to feel loved and lack thereof/ selfishness in society.

I do think that some of the things you mention are good things to do administratively, but it will never be substitute for God, morals/lack of morals culture and society. Much of it deals fundamentally with to choice to love and care for other people (or not). There are lot of people who have mental disabilities, mentally diagnosed problems or who had drugs and addiction problems and have learned to cope or overcome the adversity of it and are good people some even better for their circumstances giving them real wisdom and authority over their past struggles.