The more life choices that are made criminal, the more criminals society will have to deal with, including financially. Criminal laws, in this sense, should be reserved for life choices that hurt others. The argument that drug dealers hurt others could be applied to those who sell alcohol, tobacco and highly processed foods that are associated with obesity. These things are relative, and though they may be social ills, they should not be made criminal on that basis.
Laws that impose prison sentences on substance misusers simply fill up prisons but do nothing to address the problems they have or cause. Many people become drug users in prison because drugs are one of the main currencies and sources of power inside. The less criminal drug taking is, the fewer drug criminals there will be, and themarket price will come down making it less lucrative for drug dealers. Similarly, drug users will resort to less petty crime to fund their habit.