I got my CCW permit some time ago, but after practicing carrying for a while, I stopped carrying where I live, because I live in a very safe area. I only put it on when I was going into the city.
But, I assume Boulder is pretty safe. If I am to be able to defend against crazy mofo's like that guy, I will have to start carrying all the time. I have a buddy who lives near me and who has a CCW, and he says he never leaves the house without his gun. His gun is just part of his every day outfit...he's been doing it for 15 years now...but he's never fired a shot, of course.
But, this is another issue that will never be solved. People who fear guns are pretty irrational when it comes to that fear. In a past debate about the VTech shooter, someone actually said a shootout would have been worse. Apparently good guys killing bad guys is worse than a bad guy carefully and deliberately hunting down innocent people. The Boulder shooter was carefully hunting people. There was a policeman in there, so there is never a guarantee. But, at least if there is a good guy with a gun, people stand a chance.