Excluding someone else from a group doesn’t make someone an asshole. Every group has one or some thing(s) that separate them from the rest, otherwise they’d never have formed a group. Maybe it’s a vision, or a goal, or a belief, but there’s something that holds the group together. Contrary to what you’re saying, it’s integral to the cohesion of that group to exclude people who will not fit well.

There are countless examples of this phenomenon throughout history. Take for instance, the formation of the USA, the Catholic Church (Great Schism, Protestant Revolution, etc.), the American Civil War, etc. On a smaller scale, I know I’ve worked with people who would be a good fit on one team, but don’t match the culture of another. Or people who are very passionate about something, but wouldn’t do well in a group focused on something else. Sometimes, even, people have the same ends and such different means that they cannot coexist in the same group. You can see this with sports teams; everyone wants to win games, and some players or coaches don’t fit on certain teams because their idea of how to win doesn’t align with others’.

The reality is not everyone fits into every group. Trying to force that will yield a lot of resentment on both sides, in my experience. Much better to nip the problem in the bud.