To lose a part of a nation to a foreign power should be the decision of the nation of a whole, not just those who have been singled out by that foreign power.
(Opinion of NI people irrelevant)
I believe there was a bit of an altercation in the U.S. in the middle of the 19th century when a number of States decided to go it alone - or am I imagining it?
Was it an act of fascism on the part of the Union to impose their will on the Cessationist States?
(Opinion of inhabitants irrelevant.)
The seizure of the six counties was an act of force; first a softening-up campaign my British military thugs (The Black and Tans and The Auxiliaries), then a threat of invasion (within 2 weeks) if the treaty was not signed - was this not fascism?
The new administration in Northern Ireland was set up to represent only two-thirds of the population, openly declaring that Ulster (sic) was to be 'A Protestant State', and keeping the Catholic third down by anti-Catholic riots (I know this to be a fact through the experiences of members of my family in Derry in the 1950s) and police brutality backed up by the constant threat of British militarty intervention - was this not fascism?
The Civil Rights protest marches at the end of the 1960s were met with police baton charges and anti-Catholc stone-throwing mobs - was this not fascism?
The Northern Ireland State was born and upheld out of State violence and threats of violence (fascism by anybody's description) and therefore cannot be said to be a democratically established entity.

(So their votes can be ignored and they should be forced to accept a union.)