The first and most basic reason that marijuana should be legal is that there is no good reason for it not to be legal. I mean, why is it illegal when alcohol and cigarrettes are legal? They've caused more harm to people than marijuana. Period. People deserve the right to make choices for themselves. The government may have a right to limit individual actions if the actions pose a significant threat to themselves or someone else. But this argument does not logically apply to marijuana because marijuana is far less dangerous than some drugs which are legal, such as alcohol and tobacco and other actually prescribed meds. so, people should have the right to decide whether or not they use marijuana. The government should not tell people what to do as long as they're not harming others.
The second reason that it should be legal is that it would save our government lots of money. In the US, all levels of government (federal, state, and local authorities) participate in the "War on Drugs." We currently spend billions of dollars every year for prohibition alone. These people get locked up in prison and the taxpayers have to foot the bill. We have to pay for food, housing, health care, attorney fees, court costs, and other expenses to lock these people up. Quite expensive.