the reason that it is illegal is because of many reasons, 1 racism minorities (mexicans) brought the custom to the us white people used this as a way to control them or oppression. 2 Henry Anslinger was the drug czar from the 1920's -the 60's he hated pot. ANy way there is a couple reasons..... you should rent the movie grass and find out more for your self. It is a history of pot in the us! also i thought what i wrote before in this thread waere some reasons too.