Why is that a given without any thought of the consequences?
Heroin and fentanyl addictions ruin peoples lives forever, many regret ever taking it and wish they could escape the cycle of addiction but cant no matter how hard they try.
One reason they cant escape is because fentanyl use is so widespread and normalized the option to return to their old lifestyle is always extremely easy.
Freedom to take fentanyl and live on the street isnt freedom, its quite the opposite. Go walk around the tenderloin or pioneer square to see what this "free society" looks like.
Addiction is a problem, and it's a problem now, even with the harmful substances being prohibited. The fact that fentanyl and heroin are criminalized doesn't make anyone less likely to end up using them; the criminal penalties just make them even more dangerous to use. You're assuming that legalizing / decriminalizing fent and h possession the addiction situation would get worse -- I'm not convinced that is true.
If we legalized / decriminalized the possession of all drugs including fent and heroin, then people using them would not suffer criminal penalties for being caught with them. Oftentimes it's social factors like incarceration that make it doubly hard for addicts to escape the cycle of addiction. You are caught using and so you enter jail, and catch a felony on your record, making it even more difficult to land work. Or you end up with trauma from being imprisoned, further damaging your mental health, further driving you to escape with your drug of choice.
Long story short, prohibitionism doesn't really work in the sense that criminal penalties don't really deter drug users from using drugs. It just makes it even more dangerous to use the drugs!
1. addicts can't get predictable, reliable, pharmaceutical quality drugs. Street drugs aren't predictable, and cause overdoses because of that
2. addicts become criminals because of high street prices, leading to all sorts of associated crime
3. illegal drugs lead to massive profits for criminal organizations
4. people suffering from terrible diseases die in agony because painkillers that would work on their pain are illegal
5. people who suffer from chronic pain, which is not diagnosible, are forced to turn to street drugs
6. legalizing heroin is not going to tempt me to use it. Is it being illegal stopping you from using it?
7. being an addict is punishment enough. Why does anyone think punishing them further will improve matters?
8. consenting adults have a fundamental right to their own bodies. As the pandemic showed, our government is not very good at determining what drugs are best for people. It's more politics than science.
Committing a crime while on drugs should be a crime - the drugs should not be a valid defense.