A friend just posted a link to an article on a similar topic to my Belief and Assumptions series, only much better-researched. It takes my line of thought a few steps further, explaining how peoples' "deeply-held views" (i.e. assumptions, in my terminology) affect how we view facts. The results were pretty scary. You should read the article, but in a nutshell, peoples' preexisting beliefs change how they view and believe the same (factual) evidence, and the manner in which it is presented can also affect their reactions; people accept evidence that confirms their beliefs, and look for ways to disprove evidence that contradicts them. This is distressing. How can we argue objectively if we're able to twist the facts to fit our preconceptions? Now I understand how two people can leave a debate each being more convinced of their own position than when they came in.
Given their lethal effect on objectivity and consensus, I'm starting to think assumptions should be avoided whenever possible. I say "whenever possible" because, as I already argued, quite a few basic assumptions are needed to function in life. Hold on loosely to your convictions, no matter how right they seem to you. The only exception I make is for my belief that God created all things, that He sent His Son to die so we won't be separated from Him by sin, that He is coming back to cement His reign over all things, and that His love is better than life. Happy Easter!