Afghani Heroin

The US is being highly critical of Afghanistan's ineffectiveness in curtailing the heroin that comes out of the country.  They're being told to eradicate the poppy farms in the country, the only thing that stands between poverty and abject poverty for many farmers.  Why doesn't the western world start buying the opium directly off the farmers?  It's not as if the only use of opium is for illegal heroin - medicinal morphine and other opiates are a massive industry.  In one fell swoop much of the illegal activity would no longer be criminal, the industry could be regulated and one of the world's most desperately poor countries would be given a serious income that could help its people.