Look over there !
It’s not their own defence - there is no aerial threat to Ireland except the one made up by those with vested interests - & the dublin zoo “meerkats” who watch too much TV. If the UK govt decides Irish airspace is a threat corridor to them then they should police it & pay for it. The biggest “threat” would be an air to air collision with an airliner or similar catastrophic mishap involving civilians by a fighter more than likely by a homegrown operator or far less likely by one of a neighbouring state -and that increased risk is precisely why Ireland should not squander tax payers money on a deluded doomed project to protect UK airspace. Only an idiot would spend vast sums of money on something already provided competently for free for which there is no actual need .