1. In it's pure form, it is not that bad. Notice I say "in it's pure form". Modern day black market marijuana is usually laced with other things to make it harder. The marijuana of today is much more potent that what folks were smoking in the 60's and 70's.
2. Taxes, taxes, taxes. We, as citizens, could stand to make tons of money a year from various taxes placed on marijuana. Not only that you associate everything that a big busines can contribute. Property taxes, sales taxes, creating more jobs, the general impact on our economy would be tremendous and positive, to say the least.
3. Help the justice system. Legaliing marijuana would free up at least 40% of the justice system to focus on other crimes which are much more serious. Plus, all of the many deaths a year related to the black market sales of marijuana would cease and free up the street patrolling officers to be in your neighborhood more, rather than stuck processing evidence, arrests, and everything else a marijuana arrest has with it.
I see no other better solution than the complete legalization of marijuana. Write your congressman.