This can be a huge challenge in life as groups of people form all over the place and most of those groups actively exclude outsiders. No matter how open or closed the group seems, they will always ultimately boil down to exclude those who don't think in a certain way.
This is partially a human issue, as we are more comfortable with those that think in ways we appreciate and don't appreciate those who might truly stretch our thinking. We also all tend to "not suffer fools well," though the definition of who is a fool is largely in our own head rather than a true, firm fact.
Consider this next time you are snubbed from some inside club or if you do the same to someone else. Are internal concepts playing out or did the one scorned really deserve it? I would be most of the time it is just our own minds at work and not really as much stupidity on the other end.
People really can be stupid at times, but some of that can be changed if we will learn to listen and identify things a lot better. Honing our own communication skills is also quite valuable.