Whitney abused, asides from illegal drugs such as cocaine, prescription drugs, which are legal. It's not such a cut and dry matter.
Also, legalization of marijuana means less crime. As long as some drugs like Marijuana remains illegal, the US government is losing billions every year fighting the crime syndicates who sell marijuana. If this were legalized, it can be monitored, regulated and taxed and there would be no more threats of huge crime syndicates ranging from the Mafia, to Hell's Angels to many South American crime syndicates, the crime would go way down, as well as violence.
I do agree that some drugs which are very dangerous i.e. cocaine should not be legalized at all.