Restaurants are private property. If we were still living under the U.S. Constitution, owners of private property would be able to choose who shall and shall not be allowed on their private property.
Applied to the particular situation, you'd have smoke-free restaurants booming to cater to that segment of the population, leaving the old-smoker restaurants to cater to that niche. And it would all happen without coercion ... and without regulation.
Unfortunately, liberals couldn't wait for free people and free markets to react ... and instead decided to impose regulations on owners of private property to cater to only a specific segment of the population - the non-smoker.
BTW, I am not a smoker.