I was thinking the same thing -- meth. People under its influence do crazy, stupid things. It doesn't take long for a meth user to be reduced to an idiot, from what I have heard. Very sad and a little disturbing.
In my younger days I worked in a psych hospital and helped take care of various kinds of drug addicts. You are correct about the tweakers-- there is absolutely nothing that will extract your soul from your body faster than crystal meth.
The order of destructiveness, from least to most, is roughly as follows:
I left mushrooms, acid, and mescaline off, as those hallucinogens are not really drugs of addiction, but more an occasional adventure for people whose real problem is one of those listed above.
Also PCP ("angel dust") is in a category by itself. Nothing makes you crazier or more dangerous while you are using it, but I've never seen someone become addicted to it to the point of regular usage. I would guess for most people, once is enough, if you live through it.
A meth addict will do ANYTHING to get more drugs. They will sell their children, kill their mothers, share needles with 120-pound tubercular purple-splotched AIDS victims, and (whether male or female) prostitute any orifice of their bodies to anyone, anywhere, anytime. It is a bad, bad drug.
I'm for legalization of marijuana, decriminalization and medicalization of almost everything else, and the death penalty for all dealers of any quantity of methamphetamine on the first offense.
-ccm