Why can we not be sober?

In class yesterday, we discussed drunk driving and the professor asked "How many of you have driven under the influence?" and I was the only one that did not raise my hand. Yes, I recognize that I'm at a school where people drink heavily. However, I am continually surprised at how people take social responsibility so seriously with certain things (poverty, the environment) and so flippantly ignore it with other things (drunk driving, sexual activity). Maybe people feel responsible for collective problems but not for individual problems. It's a lot easier to be responsible for something where you individually cannot make a huge difference so the responsibility is diffused over a large group of people. Individual responsibility, on the other hand, dictates major lifestyle commitments which would deny individual pleasure, which is much more difficult than tossing some paper in a recycle box and thinking you've done your part to save the earth.