Personally I think it had more to do with corruption than anything. The CIA was happy to profit off it. The anti-drug people loved it, particularly those who were against cannabis. anyone who hated hippies. Anyone working against the antiwar movements. Those against hemp were happy. That's a lot of money just there. Politicians could use it to demonstrate a hard line stance against crime. Or just use it to target particular groups.

Then theres the people lobbying for anti-drug laws to expand the prison population. Lawyers and respective district attorneys that were happy as well.

The drug war was basically a felony printer as well. This made all sorts of social problems including unemployment / housing even more problematic. It tore apart families and still does. Meanwhile other legal drugs (opioids in general) flourished.

Then there's the overdoses / poisonings because the source and distribution networks are utterly motivated to mess with the supply.

The truly stupid aspect is that drug use has not significantly decreased. The whole "war" aspect was a complete failure. So it wasn't a good investment anyway.

So many parallels with prohibition. Government poisoned that supply as well and killed thousands.

Just say no. Indeed.