Why people hold opinions:
People will hold an opinion because they want to keep the company of others who share the opinion, or because they think it is the respectable opinion, or because they have publicly expressed the opinion in the past and would be embarrassed by a “U-turn,” or because the world would suit them better if the opinion were true (Whyte, 2004).
That's a quote that leads off Robin Hanson's paper called Enhancing Our Truth Orientation (pdf). If you're interested in issues of bias, truth, and particularly self-deception, it's required reading.
The opening sentence: "Humans lie and deceive themselves, and often choose beliefs for reasons other than how closely those beliefs approximate truth. This is mainly why we disagree. Three future trends may reduce these epistemic vices."
One trend that may reduce these epistemic vices is increased documentation and surveillance. It will soon be very inexpensive to video and audio record everything that happens in our lives. It is harder to lie or self-deceive when every word you have ever uttered has been recorded and time stamped.
Many bloggers voluntarily document their beliefs in a medium (the internet) that is public and permanent. A large repository of documented beliefs over time reduces the blogger's ability to self-deceive, and contradictions or hypocrisies are more easily exposed.
For example, a couple weeks ago I expressed my displeasure with the label "Spiritual but not religious." I described why I think it is a phrase too fuzzy for its own good. And yet, 3.5 years ago on this blog, I claimed the "spiritual but not religious" label for myself! I am forced to admit I've changed my mind.
Sure, disclosing your beliefs as you form them can leave you vulnerable, perhaps requiring embarassing about-faces, but ulitmately I think "intellectual transparency" of this sort leads to more honest living.