Excellent questions, and big 'ifs.' If it can be scientifically proven that smoking sickens non-consenting people around the smoker, the product should be banned, just as if it was benzene or some other forbidden chemical. OSHA would kick in where the employees are concerned.
On the other hand, if it merely offends non-consenting people, smoking falls into the category of BO or farting or excessive perfume- disgusting and a business would be wise to ban it or segregate it within its doors, but no need for the law to intervene just like they don't intervene with perfume that makes you gag.
The question is ultimately a scientific one that both sides seem to be avoiding: is "second-hand smoke" a legitimate health hazard, or is it not? The reason both sides are avoiding the science is: yes, cigarette smoke probably is as dangerous as a lot of other substances that are banned, so the casinos and bars and other businesses that benefit from smoking don't want to go there. But... a lot of those substances that are banned based on weak evidence having to do more with lawsuits than science, so the lawyers and activists who make their living banning this and suing for that don't want to go there either!
That's why this issue remains, so to speak, up in the air.