Putting aside that I’m already married (to a non-smoker, non-drinker, non-drug user)…
In theory its a deal breaker. But if I met a great guy or I heard of a great guy, it would be something to consider. Also, is he a casual smoker? Like 1-2 times a month when he gets together with some friends or a pack a day-er? Makes a big difference.
I think its easier to compromise on a flaw after you know the person. Many “flaws” (real or imagined) go out the window.