Bruce Schneier asks what lessons we can learn from the shooting in a Colorado movie theater, and answers the question with admirable good sense:
The rarity of events such as the Aurora massacre doesn't mean we should ignore any lessons it might teach us. Because people overreact to rare events, they're useful catalysts for social introspection and policy change. The key here is to focus not on the details of the particular event but on the broader issues common to all similar events.
Installing metal detectors at movie theaters doesn't make sense -- there's no reason to think the next crazy gunman will choose a movie theater as his venue, and how effectively would a metal detector deter a lone gunman anyway? -- but understanding the reasons why the United States has so many gun deaths compared with other countries does. The particular motivations of alleged killer James Holmes aren't relevant -- the next gunman will have different motivations -- but the general state of mental health care in the United States is.
Even with this, the most important lesson of the Aurora massacre is how rare these events actually are. Our brains are primed to believe that movie theaters are more dangerous than they used to be, but they're not. The riskiest part of the evening is still the car ride to and from the movie theater, and even that's very safe.