Economics....not religion I'd say. Half the Prods and Presbyterians were just as skint as the local Fenians. The monied Masons of Malone Rd, South Belfast, never ask what side of the mythical fence the other is on....No transubstantiation, or immaculate conceptions, or celibacy discussed at Downroyal or Royal Portrush.
The Protestant needed religion to keep himself in line....the Catholic, to keep his neighbour in line.....Nietzsche.