Well, I'd be okay with people smoking cigarettes if non-smokers literally never had to breathe in their second-hand smoke. So, if someone without any children lived in a single-family home (as opposed to an apartment building or complex) and never left for long enough to need a smoke break while out in public—I'd say sure, go ahead and smoke, that's none of my business.

How many people does that describe? How many people can truly predict they will never want kids? How many people never need to go out during the day, now and forever in the future?