"Man is not a rational animal, he is a rationalizing animal"
So said noted science fiction author Robert A. Heinlein. Here is my take on it.
We always appear reasonable to ourselves. We can always find a good reason for even our worse behavior. Our first impulse when something goes wrong is to provide a convincing excuse for our choices. We attempt to explain or justify our own behavior and attitudes with logical, plausible reasons, even if these are not pertinent or true.
This rationalizing does not operate at the level of our own behavior alone. We, as social animals, are prone to adapt to the reality as others find it. We tend to conform, even if, when rationally examined, the reality of the group does not make sense.
The non-conformists and the dissidents who openly oppose dominant social attitudes and ideologies are not necessarily more correct or more rational. But we might take their criticism as an opportunity for honest self-reflection and examination of even our most dearly held views of ourselves and our society.
If there's one thing the fields of sociology and psychology have made clear, it's that humans are self-perpetuation machines first and thinking machines second. What limited capacity we have for thought is often muddled by our impulses and frailties. We are capable of overcoming these limitations, but it takes a lot of effort.
On a related note, check out this cool psychology blog: http://www.spring.org.uk/