Nope. The most appropriate comparison would indeed be '60s, but it would be the 1860's.
The Union denied the validity of southern secession since they asserted that the relevant "people" who had the right to determine their government by majority vote was the "people of the United States," not the people of each State individually. Since the people of the United States had not agreed to secession, it was invalid, and the desires of the people of each State were just irrelevant.
Similarly, the IRA since its beginning has considered the relevant "people" to be the people of all Ireland, not those who happen to reside in the North. Since presumably the people of united Ireland are against a separate Northern Ireland, what a majority of those who live in the North want is just as irrelevant as what those in South Carolina wanted in 1860.
Except of course that in 1860 SC a majority of the population were chattel, which adds an additional layer of illegitimacy to the vote for secession.
From a purely logical standpoint, it would be just as reasonable to assert that the relevant "people" are the residents of the British Isles, of whom the Irish are a distinct minority.
Nobody seriously believed that the IRA was going to re-unify Ireland, the republic gave up on that years ago. It was a nice marketing gimmick for the US on St. Patrick’s day, but nothing more.
The protestants got away with slaughtering Catholics for 4 years before the IRA became a force.