It isn't as if we didn't try to ban alcohol. The stuff was deemed to be enough of a scourge on society that we criminalized it for many years in the early 20th century. It's just difficult to ban an addictive recreational substance once it's been legal for so long. The arguments for banning alcohol are much stronger than the arguments for banning marijuana.
A good point, yet the hypocisy continues. Works along the same line as you can take a girl out and spend lots of money in an attempt to end up in bed with that person, yet prostitution is illegal.