It would have been far cheaper just to buy the heroin...

From The Daily Mail:

The West is losing the heroin war in Afghanistan – ten years after Tony Blair pledged that wiping out the drug was one of the main reasons for invading the country. Despite spending £18 billion (1) and a conflict which has so far cost the lives of almost 400 British troops, production of the class-A drug by Afghan farmers rose between 2001 and 2011 from just 185 tons to a staggering 5,800 tons... (2)

Some 15 per cent of Afghanistan’s Gross National Product now comes from drug-related exports – a business worth up to £1.6 billion each year, it was claimed.(3)

1) I can't be bothered looking up how much the USA has spent; the total is probably ten times that, call it £180 billion over ten years or something.

2) The apparent increase is misleading, all that happened is that production has gone back up to its pre-Taliban levels.

3) Wot? All that fuss, all those deaths, not to mention £18 billion quid a year down the toilet, just to get our hands on/prevent other people getting their hands on drugs which we could have bought for £1.6 billion a year (plus a bit more because increased demand increases the price, so what)? Whether we'd re-sell it (to put our domestic drug dealers out of business as well) or just chuck it in the Indian Ocean is a separate debate.

Furthermore, buying up the drugs would have been a splendid way of preventing the Taliban getting into power in the first place - it would have pitted the financial interests of yer average Afghan farmer against them, they'd have preferred to stick with the easy Western cash.