Quitting cigarettes was trivial. I decided not to buy a pack that day and then never bought another pack. That's my anecdotal contribution to the discussion.

Less anecdotally:

Opioid withdrawal, in extreme cases, has killed people from persistent vomiting and diarrhea. It has measurable physical symptoms with an understood pathophysiology largely connected to the cAMP-signaling system.

Nicotine withdrawal is far less understood, to the degree it has been classified at all (mostly in studies of mice). It certainly has never killed anyone, you're not going to shit yourself to death. They're not comparable to one another.

For me, quitting smoking was easier than quitting coffee addiction. Coffee is everywhere, cheap, and consumption is all but encouraged. If I were to smoke I take on all sorts of baggage. Much of smoking is about being a smoker which is a mindset and community that is hard to leave. Social effects can be much stronger than physical dependence.

As a substance its no where near as addicting as heroin, no one would actually ruin their lives for nicotine in case it was illegal and expensive.

a) The downsides to smoking are far longer term and harder to feel daily

b) You're surrounded by smokers, you can literally smell them smoking just by walking down the street

c) Smoking is legal. You can just go buy a pack.

I am unsurprised that quitting smoking is harder for some people, given that. But in terms of withdrawal symptoms, that's where I think heroin is probably worse. But I also don't really know. So far someone linked a Google search and an irrelevant paper.