To be perfectly clear, most addicts understand that their addiction is killing then, but caring about that pales in comparison to the addictive urge to continue using. It's not some cerebral choice- once addicted, you are no longer in control of your body, or it's urges.
With that said, we as a society do have a responsibility to protect children - free access to heroin (for instance) would be incredibly harmful to children, who have not formed the ability to properly assess risk. Allowing for unfettered access to heroin for adults is much more complicated. Given how easy it is for most adults in America to access the drug, I would argue we are already contending with many of the complicated factors of unrestricted access already. How to deal with those problems is something I don't have many good answers for.
We're all irrational actors, though. Various life events drive people towards drug use. It doesnt have to be a rational decision: a split second moment of desperation is all it takes. And heroin is just _that_ addictive.
With that said, we as a society do have a responsibility to protect children - free access to heroin (for instance) would be incredibly harmful to children, who have not formed the ability to properly assess risk. Allowing for unfettered access to heroin for adults is much more complicated. Given how easy it is for most adults in America to access the drug, I would argue we are already contending with many of the complicated factors of unrestricted access already. How to deal with those problems is something I don't have many good answers for.