Well , France did decide it owns Corsica. Many countries own disputed territories so it cannot really be argued that the situation with Ireland is black and white and beyond dispute in comparison.
I find that question perplexing as it is constantly asked of English people but not others. I have lived abroad several times and the question never arose in the media or anywhere else. These places did not have any more or less of a national identity than we do. If you are unsure of English...