Seventy-five years ago, the 18th Amendment (allowing federal prohibition of alcohol) was repealed. Should we now repeal the Amendment allowing Congress to prohibit marijuana?

Oops, it seems like the feds didn't let that pesky Constitution thing get in their way this time. Nowadays, all three branches of the federal gov't have defaulted on their duty to uphold the Constitution, and instead just cite the Commerce Clause ("The Congress shall have power ... To regulate commerce with foreign nations, and among the several states, and with the Indian tribes") to allow almost any federal laws. (Take a look at Gonzales v. Raich; the Supreme Court ruled that the power to regulate interstate commerce includes the power to completely prohibit marijuana that is grown and consumed entirely within the borders of a single state.) Even if you believe that prohibition of marijuana has been a net good thing, note that the same perverse interpretation of the Commerce Clause is what permits all the bullshit "reasonable" federal gun-control laws.

While I personally don't use currently-illegal drugs and wouldn't even if they were legal, I think that drug prohibition has been a net harm to our country, just like alcohol prohibition was. Where do criminal gangs get their money today? Selling illegal drugs. Just like the criminal mobs in the 1930s got their money by selling illegal alcohol. So, if politicians really wanted to deal with the street violence, they should bankrupt the criminal gangs by decriminalizing drugs instead of scapegoating law-abiding gun-owners.

See also http://online.wsj.com/article/SB122843683581681375.html