This sounds like an argument for criminalizing cigarette manufacture and sales. I think you could make a case for it.
But to get at the deeper point, do you think the government should have a role in regulating harmful substances or should the public have free and easy access? (Or some middle ground?)
The public should have free and easy access to these things*-- or, at least, as free and easy an access as to cigarettes or alcohol.
The government should regulate the hell out of whether these things end up in products without our knowledge (no lead paint in toys, no cocaine in coke) but if a citizen of legal age is on the lookout to buy some marijuana, ecstasy, lsd, etc, it should be as easy as buying cigarettes. The only things that should be considered are 1. does the citizen have the required amount of money and b. does the citizen have proof of age.
Now, with that should go very strict penalties about operating a motor vehicle while under the influence. It is about harm to others. (I also don't care if the government taxes these things heavily.)
It has nothing to do with harm to oneself. We all should have the freedom (potentially) harm ourselves by ingesting drugs, scarfing bacon cheeseburgers, sleeping with strangers whose sexual history we don't know, joining the army, wearing a wingsuit with no parachute, climbing mountains with no guide rope, or doing missionary work in Afghanistan. Or all of these things, if we wish, although I don't think we should be able to do numbers 4 and 7 concurrently.
I can go to the store and buy a rope, a straight razor, and sleeping pills at any time. I could commit suicide with any of them if I wanted to.
Should these things be controlled?
*I am willing to modify my position if it were shown that any particular drug makes people prone to the kinds of attacks on others that crazy oldschool drug propaganda films claim-- killing babies, for instance, but the harm to OTHER people is the key.