Of course, trying just to prevent tragedies isn't enough. What we really need to do is to build lives that are safe and fulfilling and happy enough, not just for ourselves but also more generally in our society. That means doing good in small ways in our daily lives, but also making good decisions in the huge national and global issues. Ouch, that's sounds like too much responsibility. Maybe I'll try to do a lot of good in the small things, but let evolution be the ultimate arbiter on the big ones. In that way, I won't get overwhelmed and give up on both fronts. I should probably go do something worthwhile right now.
Update 11/26/14. Here is a summary of a report on Adam Lanza's mental history. It faults his mother for not taking important measures in light of his mental situation and its deterioration.