When I was young, it was the conventional wisdom that Ireland would achieve inevitable greatness if only the Republic and Northern Ireland were reunited. The mechanism by which this greatness would be attained was never explained. The proposition was so self-evidently true that to voice any doubt was to expose oneself as a knave or a fool.
Well, we've come a long way since then. Nowadays, there are very few people in the Republic of Ireland who seriously advocate for a united Ireland. The disadvantages of uniting are obvious, the advantages elusive.
The two parts of Ireland could be united only if a majority in both parts wished it. There appears to be no possibility of that happening for the foreseeable future. A solid majority in Northern Ireland -- many Catholics as well as almost all Protestants -- favor remaining in the UK. And I believe that if the citizens of the Republic were faced with a referendum tomorrow requiring an up/down vote on actual, immediate unification, a majority would vote "no."
But let's assume for the sake of discussion that a majority of voters in both parts of Ireland were to vote for unification; what then? One must assume that there would still be a very large "no" vote by Unionists in Northern Ireland. Perhaps most of these voters would reconcile themselves, however reluctantly, to living in a united Ireland. But a substantial percentage of Unionists/loyalists would never accept being ruled from Dublin. And some portion of those would resort to violent resistance to the new order.
Thus, the first and most serious disadvantage to unification would be the eruption of a new round of Troubles, with loyalist paramilitaries making war on Catholic/nationalists and the Dublin government. These new Troubles could drag on for decades, even generations. They would not be confined to the territory of the former NI but would involve bombings and other terrorism directed at targets of opportunity throughout Ireland. Just as the UK government could never defeat the IRA, the Irish government would not be able to defeat the the new UVF or UDA. Moreover, with the separation of NI from the UK and its incorporation into a united Ireland being a fait accomplit, it is hard to see how any political resolution would be possible.
The second disadvantage of unification is that it would devastate the economies of both parts of Ireland. Thirty years of the Troubles left the Northern Ireland economy in a shambles. The province is totally dependent on massive amounts of aid from the UK. In a united Ireland, the Dublin government would have to pick up the tab, which would bankrupt the country in no time at all. Moreover, with NI currently at peace and a political settlement in place, there is at least some hope that NI will be economically self sufficient some day. That hope would vanish in a united Ireland plagued by perpetual loyalist violence.
So, the major disadvantages are obvious: (1) intractable political violence, and (2) economic collapse.
