I had a buddy who's life was almost completely ruined by drugs and alcohol. He went to rehab and has been a fine member of society now for the past 7 years. Jail would have been the straw that broke the camel's back for him. He'd probably be dead by now.
I agree with you 100%, but tell that to GW's new "Don't treat'em, just jail'em" drug czar. And we thought we couldn't do any worse than Generalissimo McCaffrey, we were wrong.