Human beings are not always rational.  We are tribal and emotional, preferring to unite with those who think like us over attempting to understand those who don't.  This, however, is at the heart of many of our problems, both personally and professionally.  When you give people the benefit of the doubt, you set yourself up for success, simply because you start from the premise that others, even those with whom you disagree, have good intentions.  It is simply the approach that varies, and that can always be worked out.