Premise the 1st: Given the nature of the state...The state will either prohibit or Tax drugs.
Premise the 2nd: If the state taxes drugs, they will make lots of money from taxing drugs.
Premise the 3rd: If the state makes lots of money doing something...it will attempt to maximize revenue ahead of most other goals.
Conclusion: Legalizing drugs would cause lucrative drug taxes, which would increase the number of addicts based on observed behavior of governments.
Thought from this post @ CoyoteBlog, and liberal consumption of Offsetting Behavior's frequent smoking analyses.