MC Gooch said:
How so?
Well when you support a team, share in their joy, feel pride and glory and boast to your friends etc... it's only not arbitrary if the team reflects you personally in some way.
Supporting your son's soccer team isn't arbitrary. He's your son, you have control over how motivated he is, how well coached he is, how directly supported he is etc. But supporting the Warriors just because they happened to be born on the same land mass as you? And half of them don't even have that much

It's pretty arbitrary. It doesn't reflect you, your values, your strengths etc one iota.
If other people choose another variable with which to base their arbitrary allegiance, then so be it