As I am not from Norther Ireland I don't know how correct this is, but I have always looked upon it as a problem that was created by the drawing of country lines which in my head is very comparable to the Sudetenland during WW2, (Not comparing UK to Hitler or Nazis), in which the UK had a sort of mixed bag that had a large content of English citizens and people that wanted to be in the United Kingdom, so that they sort of HAD to take it for themselves. And although some citizens resisted (IRA) they still made the right choice.