Reason 3 is really the only one that matters.

Reason.tv: 3 Reasons to Legalize Pot Now! - Hit & Run : Reason Magazine:

"As the United States enters its 72nd year of marijuana prohibition, it's time to consider legalizing pot once and for all, for at least three reasons:
1. The tax revenue and savings in law enforcement costs...
2. It's going to happen anyway, so why delay the inevitable...
3. Keep Your Laws Off Our Bodies."