And being under the influence of marijuana while operating a vehicle is illegal everywhere, even where it is a legal substance. DUI is not limited to alcohol.
EDIT: my position, which would typically be described as extremely pro-drug, is largely due to my discomfort in treating medical personnel as de facto agents of the government on drug policy without requiring medical experts judge at trial for drug crimes like they do for malpractice proceedings. Essentially you have the people who decide what drug use is legal and illegal having no competent oversight -- we are in a nation with functionally no drug laws to the influential or wealthy enough to locate a doctor amenable to their suggestions, so why not at least offer everyone the same freedom until a more coherent policy is found?
Some may refer to this as "microdosing" but I think this gets it backwards. If anything, drugs are useful tools that can also be "macrodosed" by those wishing to experience extreme effects.
I would like to live in a world where all drugs are legal and people can use them to enrich their lives, not just escape from them.
But of course, there is a connection, because people tend to force that high so much, that they just do too much ... and also forgetting that you can't be "high" forever. What goes up, usually comes down.
(just being pedantic, in general I agree with you)
... I think OP was using those examples because they're the stereotypical horror story drugs, but their analogues are everywhere.
You say you don't understand why drugs are illegal. I think this is your core misunderstanding.
You are not the most anti-drug person I can find. I've never used alcohol or cigarettes (I didn't even use painkillers when my four wisdom teeth were taken out), and spent the majority of my life admonishing the use of caffeine.
I am not even anti-drug compared to most Americans. A substantial portion of America believes that using drugs (illegal drugs only, of course) is _morally wrong_. That is why they have favored sending people to prison instead of rehab. Because it is a violation of the social contract they favor to be under the influence of such substances, and that by using them you are no longer able to execute your duties as a citizen. And you aren't. I don't want you high on meth when you vote. I don't want you high on pot when you drive. I don't want you coming down from heroin when you serve on a jury. Those actions have consequences, all actions as a citizen do, because we cannot isolate from each other. Breaking those commitments _could be_ considered morally wrong, and not just from puritans or fundamentalists.