Are people seriously suggesting that if the IRA wanted a hard border, then that wouldn't be what the EU and Democrats in the US were pushing for?
A "vote yes or we will continue to be violent" is NOT a free vote or "consent freely given" under any definition, unless it's England and the UK on the receiving end.
If there did end up being a one-sided hard border, then it would actually be the EU and anyone complaining to the WTO, who would be responsible for breaking the GFA.