I agree with your dim view of prohibition. It clearly makes things much worse. In fact, I lean toward the extreme opinion that prohibition isn't merely counterproductive, prohibition is the entire problem. Furthermore, the notion of "drugs" and all that they represent is socially constructed; only a sliver of what is believed about drugs comes from the chemicals themselves; most of it is a tradition of myths that form a sort of secular religion, along parallel lines to belief in things like black magic and curses. Drugs are thought of as possessing evil and demonic properties; they are tainted with black magic, and consuming them brings the black magic into a person's body and causes them to commit evil acts, infects their minds and causes madness and irrationality, causes everything the person is connected to to self-destruct, and ultimately kills them. Unless, that is, they are able to break the hold of the magic, renounce drugs, and perform rituals of cleansing (getting "clean"), etc., to symbolically remove the magic and show that you have been reborn as a person who recognizes the terrible power of the black magic and now wants nothing to do with it. Except that the magic can never be completely washed off; you are now an "addict".
One more thing. I think rehab causes people to die, because a heroin user is made to stop, then they are in rehab for a while, and then they get out and accidentally inject too much and overdose. When you are denied something you want for a period of time, the tendency is to make you want it more. It makes the drug into an obsession and the whole thing just reinforces the importance and perceived desirability of the drug.
I think that even users of a drug have beliefs about the drug and its effects that are myths promoted by the anti-drug side. Drugs are supposed to feel like more pleasure than 100 orgasms, right? I actually think that no drug directly causes pleasure. It's like alcohol. Alcohol by itself does not plaster a smile on your face. The enjoyment of drinking comes from combining it with an enjoyable activity. Likewise for drugs. Their effect on mood is neutral and the enjoyment comes from combining it with an enjoyable activity.
I see the rehab industry as selling snake oil. I'm sure that it has been a good business to be in with the trend to send fewer addicts to jail and redirect them to rehab instead. Going to rehab is a good idea if you need to rehabilitate your image, e.g. to get a job. I have no experience of American rehab. The whole idea seems weird to me.
I think one of the practical effects of it is that serves to teach drug users about the "addiction disease" and how to act their part in the drama. I suspect that it helps bring about the symptoms of the "disease", because without being educated about the symptoms, how would you know what you're supposed to do?
It almost seems like the message of NA was maliciously designed to induce hopelessness and defeatism, the exact opposite of what would help a person who needs optimism and confidence to make a change that might seem scary.
Anyway...