As someone who lives in the north of Ireland, comments like this make me chuckle. Perhaps it's why I am more accepting of the Horde-Alliance conflict, despite why certain players can't get their heads around the seeming illogical nature of it. Because believe it or not, it is absolutely true to life.
Let me tell you, hatred for the other is insidious and is easily transmitted from generation to generation and no amount of incomprehension by an outsider or 'letsgetalongerism' from those within the respective groups but who wish to push the past behind them is enough to tamp down that hatred. Just because people in opposing groups have commonalities does not mean they are suddenly going to prioritize those commonalities over their grievances against the other group.