addiction is a factor, but it's never simple
Drugs cost money. Crack, in particular, is a damn expensive habit. During binges, it's easy to spend $1,000 a day on rock. (Double that if you're entertaining.) Even homeless crack addicts somehow manage to spend an average of $200 a day. (Meth heads and dope shooters spend less, on average.)
Most addicts blow their own money first. If they were well off when they started, this can take from a few months to a few years. If they were not well off, this part takes less time. (And, yes, BonanzaBob, the shame of having blown one's wad is compounded by the depression of withdrawl.) Most addits then scrape together whatever they can beg or borrow or steal from friends and family. When those resources are also exhausted, addicts commit crimes.
Most addicted women begin with prostitution and move "up" to various scams. Most men begin with property crimes and move toward more violent crimes. Eventually, most addicts who continue using wind up either in jails, institutions or morgues.
Does this mean that all addicts are criminals? Or that all drugs users are addicts? Of course not. Most people use alcohol and moderate drugs (especially pot) recreationally without ever becoming addicts. And many addicts are able to manage their drug use within affordable limits. (You'd be amazed at how many of your neighbours and colleagues are smoking rock on friday nights, or shooting maintence levels of dope in the office bathroom. One recent study in Britian estimated that one out of every 70 young male Londoners smokes crack occasionally.)
Legalization would help. This would lower the cost of all drugs, thus lowering the pressure to commit crimes. More importantly, it would allow addicts to come out in the open, which, I believe, would compel a compassionate soceity to help far more into treatment and programs such as NA.
Crackhead