More than one thing can be causing problems in a society, and enterprising humans of lesser scruples have a long history of preying on the weaknesses of others for profit.
Enterprising humans have a long history of giving people what they desire, while refraining from judging what's best for them.
Ah yeah, fentanyl drug adulterers, what great benefactors of society.
Screaming "no one is evil, its just markets!" probably helps people who base their lives on exploiting the weak sleep better at night.
No one desires adulterated fentanyl.
No one has desire for adulteration, but they have a desire for an opiate high, and are willing to accept adulteration as a side effect.
You can look to the prohibition period for historical analogies with alcohol, plenty of enterprising humans there.
Fentanyl adulterators, market creators and resellers certainly do, for higher margin selling and/or increased volume.
The traffickers looking to pack more punch into each shipment that the government fails to intercept do.
Basically it's a response to regulatory reality, little different from soy wire insulation in automobiles. I'm sure they'd love to deliver pure opium and wire rodents don't like to eat but that's just not possible while remaining in the black.
Worse than enterprising humans are authoritarian humans who want to tell others how they should live, usually also exempting themselves from their rules.
They also prey on the weaknesses of humans and social appearances to do things for a "greater good".
There's a problem and we 'must do something' and if you're against doing the something I propose youre evil and I'll label you.
The real mindfuck is that sometimes, an unscrupulous entrepreneur only has to play your "societal harm fighting" game through politicians and they get their way and we lose.