The problem is that responsibility comes from reason, and drugs like Fentanyl are a direct attack on your faculties of reason. A lot of Enlightenment ideals fall down when faced with hyper addictive things IMO, and we just keep inventing new ones.
Alcohol is a much more serious attacker of reason
Prohibit it?
Yeah, nah!
Provide safe alternatives
MDMA for example
A large group of people partying on MDMA is a wonderful thing.
Close to True Bliss
I highly recommend it