The government of a country is the drug lord, or is cooperating with drug lords to gain money for letting them go on with their business. A drug addict(especially the one on the hard stuff) is a drug addict, and if it is necessary evil, than the government can may as well take the money that junkies waste on drugs for herself and maybe even put it in to good use. For every kilogram of drugs intercepted by the police on the border you here on the news about, there are 3kg. allowed to be dealed away.
There are reasons to believe that one of the reasons the USA goes on campaigns in the middle east is to take away the drug trafficking business from the hands of the countries they fight with, and by doing that cut one of their enemies's biggest source of finances. And of course deal the stuff themselves afterwards.
If you want not to have junkies(in this I don't include people on marijuana, unless they let it go too far) than one of the the quickiest solutions is to shoot them in the head on a public square.
Since democratic countries don't resort to that, they have junkies and so, it's better for that drug money to go in to government's hands than the hands of that countries enemy or some independent drug lord.
Legalising drugs... well, you would still had your own state selling you the stuff. No one can tell for sure what effect, in terms of degree of the use, would legalising(complete legalising)had, and I don't see any big country gambling with that really, even though such action would if the drug use wouldn't increase dramatically by it, be a step forward for mankind maybe. You could say- here, we have the right to take any drug we want , and even though we are smart enough not to, we enjoy in the sheer freedom of the possibility. The question is, I think, how smart are we? Can we cope with such almost absolute freedom? Too many choices, for many people mean confuse.