Tobacco for the masses

Why do some people reject evolution as scientific reality given all the evidence? Why do smokers keep smoking given all the scientific evidence? To me the second problem is the one worth fixing. I still can't get over the reality that there exist doctors that smoke. That is like a geologist that believes in young earth creationism. It's not as if their life depends on finding a coal deposit - but surely the one important goal in life would be to give up smoking.