There's a legitimate argument that the unionists oppose setting up a border between NI and rUK, and it would be questionable to impose a border between the two without unionist consent. However, this can be circumvented through a whole-UK backstop. What's more, NI voted against leaving in the first place—and NI parties later campaigned on ensuring a very high level of participation in the single market upon the UK's departure. There is no majority in NI for a no deal brexit, just as there was no majority in NI for Brexit period; nevertheless, the UK, demonstrating blatant disregard for the spirit of the GFA—as well as for the concerns of NI voters—decided to press ahead with the dumbest possible implementation of Brexit, knowing full well it would screw NI over. So when some sanctimonious Spectator-fapping tit gets all pious about the GFA and the importance of consent, it may be appropriate to tell that scoundrel to fuck off with that nonsense. Such claims are made in bad faith and deserve little consideration.