I do wish to be as clear as possible that I think some hard core, illegal drugs, absolutely suck in the toll they take on society. And all things being equal, if made legal tomorrow, I do think abuse would ramp up, at least a little, and use would go up a few notches. Like say 15% of population currently uses some hardcore illegal substance, if made legal, I could see that going to around 40% usage, though mostly on experimental level. Try a few times, and get off, while abusers I could see going from say 5% to 15%.
But, I don't see "all things being equal" to how they are today if made legal. I think reality would be vast amounts of debate and hopefully sensible heads having sensible discussion. And is where mass education comes in. Not just educating potential users, but educating society about realistic impact. And hopefully, bringing in necessary perspective that shows less dark side of hardcore drug use. If that is ignored, as it is now, then a) it will never be made legal, which I'm sure means great news to some, but b) the problems we have now continue.
To correct B, then A needs to be reversed. But to reverse A, there are items that I think 'cooler heads' can conceive of to make transition as smooth as humanly possible. Like it may take us 5 years to enact legalization, and in that time, we will set up treatment centers, manifest significant well rounded educational campaigns, and decide on how controlled distribution will be, plus to what degree age of consent will come into play. All these things would help (right now) stave off serious problems we might experience, but are simply not possible if hardcore drug is perceived as, a) must be illegal, no critical analysis allowed and b) any analysis allowed must only present dark side, or is to be deemed 'deceptive.'
Keeping it illegal and keeping it 'dark,' benefits (highly) a certain faction of society, and that faction is gaining sense of power to 'absolutely corrupt.'