Carol at planningblog says that cocaine use should be "socially unacceptable" on the grounds that it supports criminals and terrorists in Afghanistan.
Leaving aside the question of whether the drug producers in Afghanistan are our allies or our enemies this year, it reminds me of the sign at King's Cross Underground saying something like: "giving used tickets to touts helps fund drugs and other criminal activities". That's probably true, but then so does buying cinema tickets, CDs and Manchester United shirts.
If we really don't want (some or all) Afghans to gain benefits from the drug trade, the best thing to do would be to compete with them.
Not that I'm recommending cocaine use - there are better reasons for abstaining than wishing to boycott the suppliers (though, as ever, see M Simon for some of the complexities involved)
Hang on a minute, I thought Afghanistan was heroin country...