All these things that I have done

It's when it turns to violence that I find it worrying, as in the Rangers/Celtic example. I would put the Irish Protestant/Catholic thing in the same category - violent tribalism is not confined to sport. It's also true that the impulse to not support the other side because they're the other side is not confined to violent tribalism (witness politics, as I said above). I just found the choice of such a particularly violent example odd.