There is a UK border in Ireland, not an Irish border - the Irish border is the beach. The UK border in Ireland was established by the UK, the vast majority of Irish people didn't want a border.
Missangrypants your comments are moronic. Ireland is very happily part of the EU, which partly exists to protect smaller as well as bigger countries and could not oversee something which threatens peace.
A hard border threatens peace as the Good Friday Agreement (peace treaty) allowed for free movement between NI and the Republic and agreed on parity of esteem for those living in NI who identified as Irish (affording them the right to have Irish passports) and those who identified as British. A hard border would clearly assert that one part of Ireland is British, and (post-Brexit) not in the EU, and therefore not Irish, so it takes away the rights of almost 50% of the population in NI. Add to that the considerable number of cross-border institutions that maintain the peace and ensure co-operative enterprises between NI and the Republic can flourish, thus embedding the peace.
Also, nobody really mentioned Ireland during the referendum. There was no bus with “what the fuck do we do about Ireland?” On it
Irish people mentioned Ireland! Brexiteers dismissed any fears about Ireland, and said there'd be no return to a hard border.
The Tories are propped up by the extremist DUP who say NI cannot be treated differently to any other part of the UK, and cannot have a different agreement. The only land border between the EU and the UK is in the Republic so w/o a hard border, there would be nothing to stop someone from the EU walking into the UK. And yet Brexiteers want to stop free movement into the UK.
Very very very big mess.