Well, it is obvious why drugs like Coke, Meth, and whatnot are illegal. They are detrimental to your health and cause extremely adverse affects to you, and the entire community as a whole. When one person has a drug problem, it affects EVERYONE in a bad way... trust me. I know from experience with family members.
Pot is illegal mainly because well... I dunno why. There is no reason for it to be illegal. Alcohol is much much worse than Pot and it is legal... so I dunno.