I believe #1 reason why the government won't legalize pot is because it cannot be taxed or controlled once it legally available. Anyone could grow pot in their backyard.

Without the ability to tax it or control growing it, there is no ability to control intake. This creates numerous societal problems: lung cancer, long term psychological problems (paranoia), addiction, greater societal malaise.

And trust me, pot is addictive. We'll all seen friends/family who passed up potential for drugs.