> but in the Fentanyl age I see people dropping like flies all around me

Fentanyl is a response to prohibition. If you have to smuggle something it's a lot easier to move 10 kg of fentanyl and cut it with something near the point of sale than to move 10,000 kg of codeine from the point of manufacture.

But then you have street dealers cutting it with who knows what in who knows what amount. They may use a 1000:1 ratio of unspecified hopefully-inert powder to fentanyl but don't mix it evenly so some customers get a 10000:1 ratio and others get 100:1 and become addicted or overdose. Or a dealer has one supplier who was already cutting it 50:1 so they were used to only cutting it another 20:1 so their customers don't complain, but then they start wanting larger quantities and find a new supplier without realizing they just bypassed the one who was pre-cutting it and are now getting uncut fentanyl.

None of that happens if anyone can buy codeine at Walmart. Or for that matter if they can buy fentanyl and know exactly how much they're getting.