Why did the UK not just let go of the north of Ireland at the establishment of the Republic. Do we really think they did so to spare the loyalists - or did the loyalists exist as protagonists for the very reason separating of Ireland; by preventing Catholicism engulfing the country and then by precluding separatist nationalism.
It is one thing for the English to divide Ireland for ideology or even for whatever tithe it could yield but it is another to prevent the whole nation's economic emergence in competition with Britain. Yet another is about defence.
Northern Ireland contained the heavy industry, specifically shipbuilding: the economic powerhouse. NI contained the deep sea ports that faced Britain and could blockade Liverpool's shipping lanes. Northern Ireland could not be allowed to fall from control. We did not want a Russian port in Belfast.
The endless dispute, and enraging violence that festered, allowed Britain to refuse independence on the grounds of never capitulating to terrorism. It suited the objective well. Conversely, for those who truly desired a united Ireland, the violence prohibited any peaceful process that could have achieved independence in less than ten or twenty years of simple but tireless campaigning.
For those who did not comprehend the true nature of 'the troubles', the snake-oil Blair (spit) had on offer was:
(a) for the republicans: the end of British involvement with Northern Ireland, for ever
(b) for the loyalists: independence from the UK but anonymity and separation from the south.
To understand how this will to occur is to understand how the regionalisation of the UK is to take place as it is progressively absorbed into the EU.
Scotland and Wales are separate regions and will deal directly with the EU (hence the currant independence shenanigans). England will be nine independent regions with a faux national government at the outset.
The UK will exist no more. That is a level of authority the EU has absolutely no need for. National governments will eventually be replaced by individual regional assemblies but for the interim this concept will not be allowed to blip on the public's radar - too difficult to sell.
Ireland (Rep. of) is to be divided into two regions. The south had Cork and Dublin. The north looks like a jigsaw in an Oxfam shop - with a big important chunk missing. That chunk is NI. The logic is very elementary.
The Loyalists cannot cry that they want to be a part of the UK because there will not be any UK - it will be gone - just a dusty twinkle in a museum to housed in the Palace of Westminster remembering the old days of the United Kingdom and British Empire.