It's also a matter of actually asking whether prohibition helps. Does it help prostitutes? Not in the least.
I'm all in favor of prohibiting theft, murder, etc., but drugs are a little ludicrous. It's obviously unenforceable, and a government will bankrupt itself trying.
Prohibiting theft works, but prohibiting the sale of stolen goods has largely failed. An even worse track record is the prohibition of copyright violations. A prohibition on suicide may be an interesting case to look into.
To me, it seems that prohibition has some complex equation to determine if it will or will not fail. This becomes even more complicate when you consider the option to prohibit with only fines, at which point it is nearing becoming a sin tax instead.
I'm all in favor of prohibiting theft, murder, etc., but drugs are a little ludicrous. It's obviously unenforceable, and a government will bankrupt itself trying.