I don't think anyone here is advocating that any of the drugs being discussed be made more easily obtainable than alcohol, especially to the young.
No, however, the "yutes" will not have the self-control or wisdom to limit their intake of legalized or decriminalized recreational pharmaceuticals. Fer cryin out loud, look at the weekly keggers on college campi, and imagine open, widely available drugs added into that mix.
I don't know what the solution is, or even if there is one. If there were some way to guarantee that the consequences of drug use and addiction could be limited to those individual persons alone, I'd be all for legalization. However, there can be no such guarantee...