Sharon Begley, the science writer, began a fascinating article some time ago on the limits of reason with these examples of "irrationality." Women are bad drivers, Saddam plotted 9/11, Obama was not born in America, and Iraq had weapons of mass destruction. Her article asks why we so often suspend our critical thinking and roll over to the irrational.
The well-worn psychological answer to her question is confirmation bias. We only look for and acknowledge information or data that supports our own beliefs. So we expected to find WMDs in Iraq and refuse to admit that there were none. Or we see all kinds of things in Obama's birth certificate that aren't there. As a result, psychologists have been documenting since 1960 that we humans are really, really bad at reasoning. It seems to make no sense, but there you go.
However recent research adds an intriguing evolutionary insight to why we avoid data and reasoning and only look for that which supports our bias. Here's Begley intriguing summary of what's going on:
The reason we succumb to confirmation bias, why we are blind to counterexamples, and why we fall short of Cartesian logic in so many other ways is that these lapses have a purpose: they help us “devise and evaluate arguments that are intended to persuade other people,” says psychologist Hugo Mercier of the University of Pennsylvania. Failures of logic, he and cognitive scientist Dan Sperber of the Institut Jean Nicod in Paris propose, are in fact effective ploys to win arguments.
See also: Selection bias.
This goes a long way to explain why we so often ignore data and reasoning and go with our emotions and our gut. We want to win the argument. It's why we look harder for flawed thinking or research when we don't agree with its conclusions.