Umfortunately social customs that later prove to be very harmful take a very long time to die out. Even within Judaism we may have certain practices that may have been instituted for health reasons based upon the best knowledge at that time, but with more recent knowledge those practices may now be known to be actually harmful. Our leaders must be able to respond to this recent knowledge and advise accordingly.
But, for sure the fact that Rabbi so and so from 100 years ago smoked is no excuse for anyone to take up or continue smoking.