Might or might not be.
However, government can probably nonetheless, in interest of public health and safety, mandate bans on smoking on any places where employees are required to work, or general public needs to go to obtain various services.
In other words, owner of premises can indeed "decide to allow smoking on his or her own property" -- just can't compel or require (or allow) any employees to work there, and so on.
I used to think that health risks of second-hand smoke were probably greatly exaggerated by opponents of smoking -- just didn't seem that great a threat. Then I read of a study on employees of bars and restaurants in San Francisco, whose health records were rather carefully followed before and after a smoking ban, which had earlier been in force, was turned off for a while. The quality of the study and the magnitude of the results convinced me the risks are real and significant.