I think the whole issue revovles around what is at the heart of our belief system.
Here are some reasons to believe something that I have come up with.
1. Undisputed facts (of course, this does not presume that because they are undisputed they are true, rather, it only means you have never had a reason to question them. It is only until someone questions something that we begin to question it ourselves, unless we are the ones to begin to question somthing that is not making sense with the current belief system)
2. Human logic (We use our logic to try and determine which disputed facts most mirror what we conseider to be true. Of course, this is not 100% correct, but we do the best we can and we pat our selves on the back for being right "most of the time"....at least in our own minds. This trust in self is fueled with the knowledge that you have your own self interest at heart)
3. Desire (We tend to believe what we want to believe. We then adopt a belief structure that mirrors own wants and desires and then defend that belief structure to the death. When we do this, I believe we know on some level that such beliefs are untrue but we also konw that defending such a belief system empowers us in some way. Therefore, we use the power of rationalization to carry on such belief structures.)
4. Trust in other humans (We tend to look up towards certain people within our society, whether they be voices from the past or present. We see on some level their ability to accurately discern truth from untruth on a consistant basis and then rely on their judgement regarding matters that are not so transparent. This trust can also stem from our own human judgement that they care for us and, as a result, are not purposefully trying to decieve us. This is why even though they may have known short comings, by in large we are unphased in placing our trust in them.)
5. Coercion (We do not wished to be shunned from what society believes, so we may adopt their belief systems. Its not that we have a desire to believe something, rather, it is simply a desire to be accepted so we may rationalize those questionable belief systems for self preservational reasons.)
Can anyone else think of other reasons?