"It would then put a stop people from the rest of he world coming here through the open Irish border."
How many people do that at the moment, then? I wasn't aware it was a huge problem (principally because getting illegally from Africa/Asia to Ireland is a bit trickier than getting from there to the British mainland).
"Ulster citizens who claim loyalty to GB should be encouraged to move to the mainland."
I imagine it's loyalty to the UK that they claim (since NI is not part of Great Britain). Why should they be "encouraged" to move to another part of the UK any more than, say, the people of Peterborough should be?