The most basic reason that marijuana should be legal is that there is no good reason for it not to be legal. Individuals deserve the right to make choices for themselves. The government ONLY has a right to limit those choices if the individual's actions endanger someone else. This does NOT apply to marijuana, since the individual who chooses to use marijuana does so according to his or her OWN FREE WILL.
In addition, marijuana should be legal because it would save our government lots of money. In the United States, all levels of government participate in the unconstitutional "War on Drugs". We currently spend billions of dollars every year to chase innocent civilians who are trying to relax.
SUMMARY: We'd have more money to spend on important aspects if marijuana was legalized.