Sorry, but that's an outright conspiracy theory you have there. The drug policies are nothing but a populist response to the public demands to "do something" by politicians who know no ways to deal with undesirable phenomena other than trying to ban it. The same knee-jerk reaction is behind many if not most policies (most famously, rent controls).

In my country there are no private prisons and no racial minorities to criminalize but the drug laws are just as bad as in the US. Actually, much worse. And if you go to the comments section under any article about legal highs on the local news sites, most people are demanding even more draconian measures, including death penalty for possession.