There are many reasons why I wish that Andy Burnham were better than he is. Quite a good summary is provided by the fact that he has been nominated by the Labour Party in Northern Ireland (yes, it exists). He may be a liberal Catholic, and that may be all we need; give me an atheist, if those are the options. But he is clearly the man favoured by those who would cement the Union by having the more Catholic working-class Catholics, plus some Protestants, vote Labour while middle-class Protestants, and some Catholics, voted Conservative.
The Welfare State, workers’ rights, full employment, a strong Parliament, trade unions, co-operatives, credit unions, mutual guarantee societies, mutual building societies, and nationalised industries (often with the word “British” in their names) were historically successful in creating communities of interest among the several parts of the United Kingdom, including between Great Britain and Northern Ireland, thus safeguarding and strengthening the Union.
If you believe in these things, the fruits of Catholic Social Teaching, then you cannot be in favour of excluding people from them by means of incorporation into the Irish Republic, which could never afford them and in which the two indistinguishable parties - Fianna Fáil and Fine Gael - are, whatever else may be said about either or both of them, in no sense part of the Labour Movement. A key reason, among several more, why next to no one in the Republic really wants a United Ireland, and most of them never even think about it.