In our generation everyone is always saying how marijuana is harmful. Actually, marijuana doesnt cause cancer, black lung, or kill brain cells. If anything marijuana helps people with medical problems.
Hundreds of thousands of otherwise peaceful, law abiding citizens are arrested each year for simple possession, at enormous cost to our society. Our prisons are too crowded, we need the money, and the regulated sale of marijuana would be safer for everybody. Americans would rather deal with shopkeepers than drug dealers when buying the marijuana they will consume regardless of its legal status. Prohibition failed in the '20s, and is failing us now.
Watch the documentary "the Union: the Business Behind Getting High". It will change your views on marijuana.