Whether a substance is banned or legalized is usually determined (mostly) by cultural and economical factors.You know that most of these substances were legal at one stage of their careers of course. So the question that comes to mind: why was it deemed necessary to make them illegal substances (or at very least scheduling them to make them almost totally inaccessible legally to Joe Public), eventually, in the first place? I cannot see this as being done just to create employment opportunities in law enforcement.
Mind you and as a counter argument: why was alcohol not banned outright and forever.
And then in just thinking: why is weed, all of a sudden, being cut some slack?
Could it be that both of the above markets just grew to biblical proportions and to a point where it was just totally impossible to keep the lid on any longer (due to many factors not least of which is the relative ease of production)?
Every legal drug has a big industry behind it, they spend lots of money lobbying politicians, and also in direct or indirect advertising in order to change the public's opinion.
This is certainly the case with tobacco, coffee/tea, alcohol and, more recently, cannabis as well (in the "western world").
Obviously this is also the case for most consumer products (from food to guns).
All of those drugs I mentioned have been demonized and then made illegal at some point in history. In fact, as we all know, alcohol is currently illegal in some muslim countries and I believe Buthan banned cigarettes not too long ago (though I don't know if the ban is still in effect).
If you asked me I'd definitely prefer a model where individuals had the right to grow their own coffee, tobacco, cannabis, opium, coca, kratom, khat, etc... Instead of giving complete control to the big players (either public or private).
But yeah, it's a complex subject, as I said there isn't 1 unique solution for everyone...
Although it would be nice if the whole world stopped wasting so many resources trying to fight a never-ending assymetrical war and started addressing the issue from a public health perspective. Or at the very least, don't give people criminal records for simple consumption or drug-possesion.