I guess it comes back to a very basic legal and moral issue. I.e. should the law assume that everything that hasn't been specifically legislated for is illegal or assume that everything that hasn't been specifically legislated against is legal?

Or to put it more simply should we whitelist or blacklist?

In the whitelist scenario one has to condone drug taking to legalize it. Meanwhile in the blacklist scenario one has to merely not condemn it.

Personally I prefer a blacklist situation.