All of the financial costs related to heroin use comes from enforcement and criminalization of heroin, hardly any of the damage comes from use of heroin.
All crime related to heroin addiction comes from the cost of getting heroin. If it was legal or could be purchased if the buyer could be proven to be an addict, then the cost would be lower and the addict would not need to steal. All of the violence from addiction comes from the ability to not get heroin legally.
OD'ing comes from heroin purity not being controlled. If all legally sold heroin was the same purity, then addicts would OD a lot less.
AID's and the spreading of disease of heroin users comes from sharing needles and lack of access to medicine. If heroin was legal or medically dispensed, then addicts could also have access to clean needles.
Addicts are forced to operate in the shadows and out of the eye of government and medical professionals. If you made heroin legal or medically accessible, then addicts could start working on getting clean or at least not getting worse.