If we assume for a moment that drug addiction is bad, a scrambled egg is your brain on drugs, then we have only so many options. We can punish then so they stop doing what hurts them, we can try to fix the cause of why they want to hurt themselves, or simply let them kill themselves. We could flog or execute folk who use drugs, the deterrent effect which leads to some very clever and very dangerous criminals, similar to locking them up in criminal university PhD programs like we find in prison, all very expensive to maintain, or try to treat them for a disease we all have and don't know we have, the self hate that causes self abuse and a need to escape deep emotional pain in the solace of mental oblivion, extremely expensive and something we need too, or we can just let them kill themselves and maybe make some weekly runs to the dump to keep the bodies from stinking up the streets. And since the first option will ultimately cost a fortune and destroy society in the process, my guess that's the reason we like that option over the rest. There is no better way for delusional self haters to destroy themselves than punishing others.
Personally, if I were running things, I would opt for prison too, but one in which you could work for drugs and use as much as you can earn. Capitalism at its finest. It wouldn't take long and the addictive gene would disappear from society, eh?