That is, the corruption of law itself - 'planting evidence'. Sure, the police still try to catch those who actually deal in them but only when they can't show that they're doing anything better (since they have targets to meet), or otherwise not solve more dangerous cases like murders.
I mean, the law could have been corrupted before then still, but it took much more effort to kill someone and blame it on another person - placing a bag of powder at some random place is so much easier!
What I'll never digest is that there are any morals involved with these laws at all. There is no other activity where a person may harm themselves that is made illegal, otherwise (and, of course, most drugs don't even come close to doing as much harm as some other things) - the death cap isn't illegal to ingest, psilocybin is, which is harmless. This, then, confirms that anyone who's truly convinced that it's to "save the children!" is delusional, and at worst mindlessly supports a minority that attempts to justifiably bypass the law in the eyes of the majority.
Countries with the worst of human rights have the most severe laws against drugs too - a coincidence?

You are confusing cause with effect. Where prohibition prevails there will be, as a consequence, more than enough corruption.
Drug laws were originally passed in the U.S. for racial reasons. It was believed that dope would lead negro men to ravish white women sexually, so dope was made illegal in 1906. Do you know what the interesting ingredient in Coca Coal (tm) was prior to 1906. It was cocaine. Things go better with coke.