No one want's to hear it, and it's about 20-30 years too late, but the effects of secondary smoke were "proved" through bogus statistics and flat out lying.
The EPA examined about 12 studies on the effects of second-hand smoke, most of them from Europe (as I remember). Of the dozen or so studies, almost all of them showed no measurable effect on health from secondary smoke. Two of them showed a very slight negative effect, and one of them showed that secondary smoke was good for you.
The EPA then turned to something called a "meta study" which was supposed to be a way of reviewing an experiment which did not give your the results you expected/wanted. The meta study was supposed to identify information that was not gathered or incorrectly measured or classified. The objective of a meta-study was to design a new study that would be more accurate. Then you were supposed to go back and do the research again, using what you had learned.
Instead, the EPA declared that the meta-study "proved" what they wanted - that secondary smoke was bad for your health. A number of scientists and mathematicians objected and were shouted down and ignored. Once this became established scientific doctrine, every researcher suddenly found very strong negative effects from secondary smoke, even though the honest studies prior to the EPA ruling showed no such effect.
A similar meta-study was recently performed at Stanford, regarding the health effects of an all organic diet - so it now appears that if you can't prove something, it's considered scientifically valid to used a meta-study to prove whatever you want.
Prior to the bogus EPA report, a lot of people disliked smoking simply because they found smoke offensive. This had no effect on public policy. Once people were told that secondary smoke was a personal issue, the anti-smoking nazi's suddenly had something to work with.
But what can you expect. Our laws are made by a generation of people whose parents did not believe that LSD causes chromosome damage.