Not that I'd reccomend anyone start speeding for fun, but the dirty little secret of addictive drugs is that most addicts kick their habit on their own. And the ones that don't kick it on their own, usually never do.
I'd say yer right for 99% of the others per my experience as a LEO and watching such crap over time. BUT Meth seems to be the worst of the worst.....extremely low rehab rate. Bad stuff that can makes ones daughter look like their grandmother in a few years. Wish I had the answers and they were as easy as you suggest....willpower.