Smoke pot occassionally and you can still choose not to smoke anymore. Drink occassionally and you can still choose to stop drinking. Shoot heroin a few times, you’re fucked. Smoke crack a few times, you’re fucked. Pain killers are in the gray area in between, so they stay regulated.
Anything highly addictive should be illegal. The stuff that you become chemically dependent on after one or two times. That’s where I draw the line. Sure it should either all be legal or all be illegal, but that will never happen so I draw the line where there seems to be a step change in magnitude of mistake vs magnitude of consequences.