Because the Puritan ethic, for over four hundred years, has abjured smoking, drinking and dancing, I have never been surprised at the hatred, venom and human indecency directed at smokers and drinkers.
The Puritan effluvium has even penetrated the argument about the effect of smoke on nearby non-smokers and nearby non-drinkers (think .08 alcohol levels).
But I would personally rather sit in a room full of smokers or be on the highway at 3AM on January 1st than to be sitting next to an empty airplane seat and see a 300 pounder coming down the aisle.
There is nothing as unpleasant as sitting for a long time on an airplane next to a person who is far too big for the seat.
I personally know many people, wonderful people, who are gigantic and would be awful seat mates. Seeing one of them come down the aisle would still terrify me.