The reason your meth head friend commits crime to support his habit is because the drugs are expensive. The reason they are expensive is because they are prohibited. The reason people kill to stake out territory in the drug trade is because the margins are fucking enormous, and every time ridiculous ideas like minimum sentencing get enacted, the margins just go higher, and the bar is raised so that you get more and more harder core people involved.
Compare this to alcohol: some subset of the population becomes addicted to it (incidentally, a rather substantial subset, compared to the illicit drug subset), but it is legal, there is quality control, the price is reasonable and there are very few people who commit crimes to obtain it (altho an enormous percentage of prison inmates were under the influence of it when their crimes were committed, again, a far, far larger subset than those who were under the influence of other, prohibited drugs when they committed their crimes).
Alcohol prohibition in the US should have taught law makers the results of prohibiting substances - hell, there remain, many generations later, crime families who got their start because of prohibition (no, I'm not talking about the Kennedys). But as others have pointed out, there are an awful lot of people who profit legally from its prohibition, like the DEA and the ATF and the FBI and the rest of the state apparatus, which never, ever gets smaller or goes away.
An ordinary person would look at a few decades of the "war on drugs", examine the costs (both financial and to liberties) and then examine the results: did the problem go away? Was it reduced? Or did it get worse, and more violent? Does having the largest prison population on the planet, about 2 million of whom are imprisoned for rather trivial drug offenses, make the country safer, or do they learn to become criminals while in prison? What's harder for a school-aged kid to get: heroin or alcohol? Anyone who sees those results and thinks it's money and effort and freedom well spent should get their head examined - prohibition is hurting an awful lot of people for no discernible upside.