There's an argument that the criminalising of it has led to the insane strains you can get these days - there was an incredibly interesting interview with a drug csar on the radio t'other day. I'll try and post a link to it.
Legalise the lot IMHO. It's a no-brainer. Imagine the funding the NHS etc would get from the tax on recreational drugs. Imagine how much money would be kept from genuinely evil people. People want to get high, they'll do it whether it's legal or not. Legalise and control it all. (Never going to...