[aidos]

Or you could take totally the opposite approach and say that the cost-benefit doesn't need to be done for any of them. They're all drugs (including tobacco and alcohol), and they can all cause issues in different ways. Let's help the people who have problems with them.

Also, you don't need to totally legalize drugs. Though I'd love to see how that might work out.

If at any point your society thinks it needs to wage a war on the way its own citizens choose to behave you might want to take a nice long introspective look at society.

EDIT Additionally the studies have already been conducted in many cases. Asked to conduct a scientific study for your country into effects of various drugs you might find that you just end up being dismissed for presenting the data [0]

[0] http://en.wikipedia.org/wiki/David_Nutt