If we avoided doing anything because correlation doesn't prove causation, we wouldn't administer chemotherapy because we can't prove it causes remission of cancer. We wouldn't have airbags because we can't prove they decrease injury. We wouldn't take measles vaccinations because we can't prove they prevent measles. etc., etc. In the real world, we base most of our decisions on correlation.
I am actually working on a public health project to enact no smoking policies, and I am not a geek that no one listened to. It just happens to be my job.
There is no need for any US municipality or state to enact a law saying organizations can eliminate smoking on their grounds, because they are already legally allowed to do that. There is no legal right to smoke, so prohibiting smoking does not violate any law. There is a legal right to breathe smoke free air though, and organizations, landlords, etc. are all legally culpable for disease caused by breathing secondhand smoke.
I realize it is easy to think this is not important; I used to think that before I read and analyzed the overwhelming amount of scientific evidence that proves the danger of breathing even small amounts of tobacco smoke, as indicated by the US Surgeon General earlier this year.
Secondhand smoke causes the death of over 60,000 nonsmokers in the US each year, and disease in many others. It costs $6 billion annually to treat illness caused by secondhand smoke. http://www.actuary.org/pdf/health/smoking_oct06.pdf
It is an extreme oversimplification to claim that anyone who wants smoke free air is some sort of anti-smoker Nazi. That is just not true, and it's a myth created and perpetuated by the tobacco industry.
It is just about protecting the rights and health of the nonsmokers. People shouldn't have to breathe other people's smoke.