It should be legal, I think it's completely illogical to keep it illegal. It has been proven that prohibition does not work (look at the alcohol prohibition in America from 1919-1933), the only difference now is that there is a HUGE social stigma against Marijuana and it's users. A lot of misinformation has also been spread which caused this social stigma to grow and grow. A lot of people are now researching into the real information though, and people's opinion's are slowly beginning to change.
I think it should be legal for over 18 year old's, regulated and controlled in a manner similar to alcohol, with licenses distributed (industrial and personal) to people who want to grow their own. Medical prescriptions should also be use for people who can benefit from the medical uses of Marijuana.