Don't assume by my advocacy of legalization that I have ever or would ever use such drugs. I've had alcohol and some pretty wild prescription pain pills after surgeries, but I'm not really interested in getting high. My main point of interest is in the morality of telling other people -- at gunpoint -- what they may or may not ingest for whatever reason they may have for ingesting it.
Drug prohibition fails the gun-to-mom's-head test, and fails it miserably. That's why I'm against it.
I'd like to add that the laws only exist as a revenue source too. Repeal the laws too. Since the 'war on some drugs' hasn't been successful, let's spend the money on upping the ante on the border or giving soldiers better amenities near the battlefield.