Smoking cigarettes very probably causes lung cancer (although I am not so sure about arterial and heart disease - the effect size is so small that it could easily be due to incomplete control of confounders), shortens life expectancy, and I personally find it aesthetically unpleasant - and I have never smoked regularly.
The supposed dangers of passive smoking are almost entirely invented (dishonestly and/ or incompetently) - other-peoples' smoke is very unpleasant, but the only real health danger of other-peoples' smoke is the acute one of people who have for example asthma which is triggered by smoke.
But maybe smoking - specifically nicotine - has psychological benefits for some people - maybe it boosts creative accomplishment?
Take a look at this video about the design team who built the Mosquito - probably the best aircraft of the 1939-45 World War
In every shot there is one or more of these conservatively-dressed design-genius chaps smoking-away like mad, on pipes and cigarettes.
Many of the most creative intellectuals were not just smokers, but heavy smokers - CS Lewis and the Inklings spring to mind, Crick and Watson's RNA Tie Club, Einstein and his pipe, and of course Gandalf and Saruman.
If we were to compare a collection of creative intellectuals 70 years ago and now the main difference would probably be that around 1941 they would have been surrounded by a dense cloud of tobacco smoke.
Smoking (especially cigarettes, because they deliver nicotine so rapidly) is of course addictive; but was smoking among intellectuals entirely a matter of addiction?
Unlikely, because nicotine is an indirect psychostimulant which probably has significant effects on boosting drive and energy and perhaps clarity of thinking - via both direct cholinergic (nicotinic) and indirect dopaminergic routes.
There is strong evidence that nictotine both prevents and treats Parkinson's disease, and perhaps also Alzheimer's disease.
Indeed, the mind sharpening effect of nicotine is very obvious, and is similar to but different from that of caffeine.
Could it be that the decline of smoking among creative intellectuals may have contributed to the decline of genius?
Could it be that we have sacrificed a human accomplishment for a longer life span?
If so, it is probably now possible to get the benefits of smoking - i.e. the nicotine - without the carcinogenic harm - i.e. the smoke.
NOTE: Thanks to WmJas, who has found some data on smoking and creative writers posted at: