The Border issue involves principles that matter to the UK and EU states
I moved from Belfast to Bray in 1976 and remember following the furniture van containing all my worldly goods, ready to present a list of them to Irish Customs.
It was a pouring wet day but the Customs officer insisted on the worldly goods being unloaded, to make sure the television set was more than six months old. Duty would have been payable otherwise.
That was a 'hard Border', all right. The permanent army checkpoints came a bit later. They were not interested in TV sets but, unlike Customs, very interested in people. Yet even at the height of the Troubles, there was free movement. It was wise to carry identification, but not actually compulsory.