I have a differing opinion. Not saying I'm right, just my thoughts:
In the hypothetical situation herione is legal in the US, the govt will put sanctions on Afghani (probably all middle eastern) herione/derivatives. The US Govt obviously knows the Taliban is in control and of course they will not allow any trade that puts a single cent in their back pocket. Hell, I wouldn't be surprised if they only made it illegal to sell herione produced anywhere other than the US.
Open herione production up to leading scientists/entrepreneurs in the States and I'm certain they will find more efficient/productive ways of making it than a bunch of starving arabs in the desert can do now.
Same goes for weed. Legalise weed and the free market will produce the dankest shit for not much more than the cost of tobacco. Say goodbye to Mexico's drug industry.