Many people think it terms of teams\team loyalty, and their team is infallible simply because they have been accepted as a member, and all other teams are wrong completely.
In addition to sports and politics, this applies to criminal gangs. From what little I've read of biker gangs, I gather it's typical behavior that if you fight with one member, you fight all members. The details of the argument weren't relevant.
Others try to judge based on merit, using their own opinions as guide, and allow that "goodness" exists in all teams, to some extent.
I tend to think this approach is better.