During breakfast I read Jerry Coyne's latest post about E.O. Wilson, a celebrated biologist who unfortunately promotes group selection in the face of overwhelming evidence against it. My thoughts next went to other highly qualified and otherwise rational scientists who believe in very silly things. There are colleagues who reject long distance dispersal despite being aware of the existence of Hawaii, those believing in immortal, immaterial souls despite being aware of Alzheimer's and the effects other organic and physical traumata have on memory and personality, those believing in the efficacy of homeopathy despite, well, everything humanity has learned about chemistry, physics, biology and medicine in the last few hundred years...
Closer to home, those few colleagues still arguing for the acceptance of paraphyletic taxa are also very unlikely to ever change their mind no matter how many fallacies and misconceptions are pointed out in their thinking. Oh, and have you heard the term Nobel disease? Many weird examples at that link. Of course, I may well also believe something really stupid but will, by definition, not be aware of that, otherwise I would stop believing it.
So sometimes one may start to wonder why science works at all if the individual scientists can be so irrational and unable to accept the evidence. You could mention all manner of technical details, but to me it boils down to the culture of criticism. Every thought and idea is dissected, criticized and tested. Every piece of writing is reviewed and may invite rebuttals.
That is what makes the difference. For every relevant question, the cranks will likely be in a minority, and no matter how influential or famous they individually are, their colleagues will crankily and publicly tear into them when they publish something that is wrong. And so science as a whole is very likely to accept only what is correct. Although it can of course be unpleasant for the individual who is on the receiving end of such criticism, the net effect is beneficial for all of humanity.