Portugal decriminalized the possession of all drugs for personal use in 2001, and their situation has actually changed for the better.
http://www.tdpf.org.uk/blog/drug-decriminalisation-portugal-...
http://www.tdpf.org.uk/blog/drug-decriminalisation-portugal-...
There's still a black market for selling drugs, but drug users can't face jail time and have a much easier time getting help for addiction
A minor problem, all in all, considering what has changed here regarding decriminalization, but thought I'd share.
I'm not saying that full legalisation of anything and everything would necessarily be better, but...
The portuguese experiment has been a huge success in terms of harm reduction, but probably less so in terms of discouraging or removing criminal activity.