"I have. And the answer is its the EU's problem. Ireland (both parts) dont want a border. The UK doesnt want a border. So its the EU's problem if they do."
Not correct. At least if you want a peaceful NI in the UK.
IF the sectarian conflict recurs, it will be mostly fought in NI and the rest of the UK. That makes the border the UK's problem, no matter who puts it in. SI won't like it either, but they are less likely to have bombs going off in their cities.
I imagine the UK doesn't want to lose NI, either... and forcing NI and SI to become unitary I will not necessarily end the violence, just whose police get shot at in the former NI... and that still might not stop bombing in the rest of the UK by those who want to free NI from I.