[Know your rights]

illegal drug use. [...] is connected to violence, irresponsibility

So was alcohol use when alcohol was illegal, but that was no argument for keeping alcohol illegal.

and a huge cost to society to handle these people medically.

There's a huge medical cost to handle overeaters, but that's no argument for government banning overeating.

Better they die of overdoses soon after they start their habits

Then stop interfering by imposing legal punishments, and let them get on with it.

[A CA Guy]

There are complete organ failures walking into the emergency wards with illegal drugs. Not to mention often aids involved with illegal medication of drugs by syringe.

With over eating, drinking, and not enough exercise there is risk.
Where I can see that coming into play will be the higher cost of getting insurance for those who are at risk by their own behavior.