This morning I appeared on  The Leonard Lopate Show, which I have always enjoyed – both as a listener and as a guest.  I was there to talk about my book, Denialism, and Mr. Lopate turned out to be vigorously opposed to my thesis – that Americans who reject the scientific method are causing harm to themselves and to the planet. He said on the air that he has a child who became seriously ill soon after having been vaccinated – and he remains unconvinced by the many studies (involving more than two million children) which have found no connection between vaccination and autism. As a father I can imagine nothing more distressing than watching a healthy child fall suddenly ill –  without an explanation or a cure. But the argument that vaccines cause autism is not only dangerous, it is deadly.  When we cling to personal beliefs – no matter how understandable they may be – in the face of overwhelming evidence to the contrary, we are in denial. And that denialism has profound consequences for society. Unfortunately, vaccination was not the only issue about which Mr. Lopate rejected scientific fact in favor of personal assumptions: his condemnation of genetically engineered food was another prominent example. He even tried to suggest that improvements in health and longevity were the cause of the population explosion in the developing world (which is literally the opposite of the truth: as a society becomes healther and better educated family size shrinks dramatically. It is one of the basic truths of demography.)  Leonard Lopate is a terrific radio host and it was a fascinating conversation. It was also, I am sad to say, a textbook example of denialism in action (as are scores of the comments left on the show's web site by listeners.)