What is "all the evidence that it can work"? Drugs are a perfect example where governments have spent a century destroying people's lives with harebrained regulation. And yet all that it has done is empowered bloodthirsty cartels in developing countries. It hasn't improved the drug situation at all, regardless how much money we've poured into it.

As far as I can tell, gambling laws don't stop gambling either. In fact, it's usually the government that's the biggest provider of gambling services (the lottery). It seems like it's more about eliminating competition than anything else.