Certainly -- I can name a dozen, each of them demonstrated using scientific methods. Asbestos. Ionizing radiation. Sunlight. Tobacco. And so forth. Each of thes

Certainly -- I can name a dozen, each of them demonstrated using scientific methods. Asbestos. Ionizing radiation. Sunlight. Tobacco. And so forth. Each of these can be shown to cause health issues in vitro as well as in vivo -- using properly designed, scientific animal studies. Right, but then you're still assuming that whatever you've demonstrated on animals will hold on a human population. If that were always true, we would never bother doing studies on humans at all. Science isn't based on hand-waving -- falsifiable empirical evidence is required. Any number of assumptions like this have fallen by the wayside over the decades, undermined by overlooked correlations that weren't included in the original analysis. You have to make assumptions to reach a conclusion. "Humans are similar to animals" is one, and "There is no other cause that can reasonably explain this observational evidence" is another. I fully agree that observational data is often abused to reach sensational conclusions, but IMO when it is done correctly, it is a vital ingredient of modern science. Pearl's book on causality is basically devoted to this topic.