America's long-standing distrust and malignance towards cannabis goes back a long way. In the 1930s the US government released a propaganda film disguised as a legitimate motion picture entitled "Reefer Madness". FDA officials through the 1960s claimed that delta-9-tetrahydrocannabinol (the active ingredient in Cannabis sativa better known as THC) would cause everything from impotence to memory loss.
Modern science tells us that recreational pot smoking is no more dangerous than tobacco smoking. Researchers now acknowledge that earlier findings of chronic (no pun intended) short-term memory loss were greatly exaggerated, and "impotence" simply means "lowered sperm counts"--an effect, less we forget, that can be caused by cell phone radiation and plain old cigarette smoking as well.
Marijuana in the States began as--and continues to be--a convenient scapegoat for the ills of the nation at the time. In the throes of the Great Depression, the US took a couple of facts about pot, exaggerated them unbelievably, propagandized the result, the effects of which still linger today in this country.
Immanuel Kant would argue that recreational drug use is a self-regarding vice, a victimless crime, a personal choice which the government should have no hand in regulating. The mystique surrounding marijuana--its image as a countercultural talisman of anti-authoritarian sentiment stuffed into a hollowed-out Philly Blunt--is largely responsible for its popularity. Much as the age restrictions (and, to a lesser extent, glamorous portrayal in the media) upon alcohol and tobacco turn many curious teens into lifelong addicts, this patina of a free-spirited scofflaw surrounding pot may have a similar effect.
Hence, total deregulation will probably result in a large upswing of first-time pot smokers, followed by a huge tapering off as most of the public finally gets to taste the forbidden fruit only to realize it's not all it's cracked (again, no pun intended) up to be. In addition, legalization of pot frees drug-enforcement officers to track down other drugs whose addictive and lethal properties are better documented. Finally, it would somewhat relieve the overcrowded justice and incarceration systems when cases for possession, use, or sale of pot are thrown out the window.
Just my take on the matter...