Most conservatives or right-wings worldwide oppose psychoatives legalization, why such unanimity on this topic? I find it strange that there is such a consensus. Do you know why?
Personnally I don't know. They pretend to be for individual liberty/responsability while honoring for most westerners the so called freedom, but in fact are more like zealous little control freaks closer to ISIS in their way of thinking...
Only Libertarians get the concept of ownership of the body by the individual... it goes to whatever-sex to abortion to "drugs".
it depends on the drugs you want to be legalized, for example the legalization of marijuana in some countries are still widely debated,
if it is about the legalization of marijuana then I can consider it ethical, because marijuana can cure many illness, it just depends on the person,
on how they use it. It can be good and bad for you if you're not responsible, it like a double edge sword

as per other drugs such as cocaine,metamphetamine,heroine. I think it's foolish to even think about legalizing that kind of drugs.
Cure, poison, it s all in the dosage... not all things legally mercantilizeable or financializeable need to be good for health... want to reduce the sugary content of my drinks? Or fat maybe? Salt... nasty it makes you drink more...
The point is that the responsability is of the individual, this is called to be adult. You decide what you want to do.
Again most of those substance have therapeutic application in certain issue to comeback to your point. But why should you care about what an adult do with his life.
If you want to look at something really disturbing is birth control pills effects in water supplies... look at estrogen residue.
Again i come back to my motorbike problem, they are noisy and unsafe and less steerable than a car... meaning that a motorbike driving is dangerous for others too.