You're making a big assumption: that the war on drugs, even if it cost no money and ruined no lives on its own, in any way lowers the number of people addicted to hard drugs and the amount of violence related to hard drugs. While I don't have any specific data, it seems pretty obvious to me that it only increases both.
I do make the assumption that a war on drugs can lower the number of people addicted to hard drugs, and from there the amount of violence related to it. But that assumption includes the way I would handle it, like forcing users to be in rehab before prison is considered.
