It can be anything by chance. A child who inhales the second hand smoke of his parents, and tries out one out of curiousity. Acute tolerance with tobacco, so the activity within the brain chemistry is a fact.
Just a teen who attends an home party where everybody is doing coke and beer and he joins in without actual knowledge because he acts without thinking. Then notices he's bubbling very fine and the brains adapt. Or group pressure which can literally be so intimidating to some that they lose their mind.
I agree with you entirely though, I hold the same mentality. But it certainly does not inherently apply to every next individual. I wish the world was this soft and wise.
What you're slightely doing is projecting your own conscientious navigation as a guideline to everyone by asserting that they're holding an equal control within themselve, similar as yours. I dare to say you haven't been extensively present into the scene of narrow-minding drugs. When you see people being introduced, then you'll see how many factors and circumstances there are involved. It's purely anthropology.
As you adequately put in other threads as well, the self and control. I'm nearly sure that you, yourself shouldn't be afraid to try out out heroin, crack or cocaine once. You'll know the high through sensing it by yourself. You won't feel the point I'm almost sure. But I guarantee you that you'll be even more amazed about how millions of people can live for adiction than you're currently doing now through the literature.
I got to understand psychedelics much better and especially their relation in curing addiction. I analysed narrow-minded drugs and mind-expanding drugs both together in this context (as well as the scenes) and just as with sensing psychedelics alone to understand entheogenic metaphors within your own mind, one needs to experience narrow-minding drugs as well to actually understand the curing potential of entheogens. It's the other half. Then you'll also see why individuals other than yourself are having no choice if they'd come in touch with it. Or why some have to live a life with fighting against craving till their death.