I think your worries are justified, but that you should not let them impact your work too much. Imagine how restricted we would be if we had to be careful about every possible bad influences our art could have? A lot of them, we could not even imagine. People may read things completely differently than what we envisioned.
If it's really a big concern for you, you could always have one or a few scenes that show smoking in a not so good light. Eg. you can have another character discussing stopping or having difficulties stopping, and it's also easy to add a little dialogue on health concerns on this occasion. Or something like that.
I do have this kind of worries too, I have plenty of unhealthy behaviors showed in a neutral or positive way further down in my comic, in particular a scene of opium smoking in a brothel, with a character that could potentially be underage or barely adult in modern standards.Tthe scene would be all ages or +10 y/o in my country of birth, but probably very badly seen in my current country, so in my head it's not too clear what to do either.