Opioids keep the top spot of addictiveness. The second place firmly belongs to nicotine. It's way more addictive than. say, cocaine.

Why not ban nicotine, by the same logic as heroin?

The key difference is that nicotine is a mere stimulant, while heroin alters your perception, it literally changes the way you see good and bad, because it's the ultimate feel-good substance. I have zero qualms about legalizing LSD, psilocybin, ketamine, etc. Likely even cocaine. But legalization of opioids would require a lot of preliminary work, to somehow allow the addicts function in a socially compatible way when badly wanting a dose.

It must be noted that a physiological addiction to opiates does not form from a first dose, and not even from the first ten doses, so infrequent recreational use is possible, given a right psychological preparation. This is similar to alcohol.

> Why not ban nicotine, by the same logic as heroin?

because nicotine doesn't increase crime rates on society.

Nicotine is also legal, safe-per-dose and easy to get.

Because smokers can hold jobs and are productive members of society. Unlike meth and heroin, nicotine does not make people attack other people, does not make people miss work, does not make people irresponsible.

It's my understanding that street drugs like Heroin were frequently cut to varying, sometimes unpredictable degrees prior to the introduction of fentanyl. So you could still easily misjudge your dose and OD due to the lack of any kind of consistency. Presumably this would also make it even harder to try to taper off the addiction gradually.