Try parts of the Midwest and Appalachia. Industrial jobs went abroad and never came back, leaving large swaths of the population in poverty and without any real career outlook beyond low end retail. Enter fentanyl. It only made most of these problems worse.
Decriminalization, not legalization, seems like a far better path to me for seriously addictive things like heroin. If it’s not combined with serious economic plans to help the unfortunate, you’ll just be further embedding an already disadvantaged underclass. Against billion dollar advertising campaigns (which will happen with full legalization), the average person doesn’t stand a chance.