You don't have to go that far back in time or that far away to see why people may be against wearing one. No one forces James McClean to wear it yet, everytime it's that's time of year again and he doesn't wear it, he gets abused by the media, fans and everyone else in between.
If people have a right to wear one then people should have a right not to wear one whatever their reasoning. Especially when the Government and Crown have allowed or told soldiers to commit war crimes and kill civilians. You only have to look up collusion in Ireland to see why McClean and other Irish people may be against wearing one.
Patriotism, Politics and Religion etc should be kept out of sport, if it is kept out then there's no issues. Just like Cenk should have kept his salute celebrations locked away.