> If something is addictive (as in actually creating a physical and mental dependence on continued use in significant number of people) - why would you not classify that as harmful?

You want to classify sugar as harmful? It's physiologically addictive (go a few days without carbs altogether and tell us how it goes).

What about caffeine?

Yes, sugar is slightly addictive for some people. It's also slightly harmful. (Go sugar free and see how your dental health improves; dropping sugar / most carbs from diet is enough for me to get back to ideal weight)

Caffeine is also addictive and if you drink enough, stopping gives you withdrawal headaches. But in my experience not drinking caffeine at all makes me just as alert as getting used to the daily dose I thought I needed before.

So yeah, I'd totally classify both as slightly harmful.

Yes, of course they are. It's well established.

But some harmful things are worth the tradeoff if you can maintain a low enough dose (sugar or caffeine)

I mean, coffee is an addictive stimulant which isn’t usually classified as harmful.

Vaping might have social and physiological benefits which outweigh the harm also.

Gwern (an active user on HN) wrote a compelling paper presenting nicotine as a potential nootropic.

https://www.gwern.net/Nicotine

Caffeine?