People aren't stupid. They learned from Prohibition that it is hard to ban a drug once it is legal and established. Hence the reluctance now to legalize marijuana. If it turns out to be a mistake, it will be hard to roll it back. That seems like an honest and fair argument to me, even if one might disagree.
But it is not the argument one usually hears from probihitionists...
Let's not forget that jails and security are a business, and the War on Drugs has been extremely good for that business.
The possibility exists that the moral posturing around drugs has sometimes been a cover for less noble aims.
That came after, not before. Given that I've heard no one defend those heinous crimes, I find that as lacking an explanation as the silly notions that scientists are advocating climate change because they expect to get grant money.