Perhaps I could add my pennyworth: in order (supposedly!) to preserve the UK Union, the DUP and some Tories in the "Conservative and Unionist Party" are genuinely concerned that there should be no regulatory differences between the mainland (and other islands around Britain), and Northern Ireland. In fact one irony among many is that there are already many substantial legislative and regulatory differences, but let's not get caught up in that.
I am generally 100% behind the EU27's position on most things, but as it happens I think both sides are being very stupid here. More obviously the UK is being stupid because the backstop need not happen, even if promised, when push comes to shove and if, two or three or four years down the line, no FTA (Free Trade Agreement) has been reached, AND no practicable technological solution (combined with other arrangements*) has been devised either. At that point the UK could just say "OK, hard border it is". There is no point whatsoever confronting the issue at this time: it is absurd to do so: the approach should have been one of "we'll assume we find some solution to this, somehow".
But I also think the EU27, and particularly Dublin, are not being rational: this backstop nonsense is the ONE THING preventing the WA being passed (in fact large numbers of Labour MPs should have defied Corbyn's - or Milne's - political whip and voted for the WA in one or more of the 3 defeated votes) ... and therefore the one thing which is inevitably going to make a hard border this November absolutely unavoidable. Denying the "hard truth" of this Catch-22 / blackmail situation is not in anyone's interest.
So IMHO all mentions of the backstop should either be ignored by the UK side, or just be struck out of the proposed WA. But of course it's far far far too late for that: one side or the other would lose face impossibly. So we're going to have a No Deal, a hard border in Ireland, and much strife (including murder) about when and how a (first) Reunification referendum is to be held. If the NI referendum - the Republic has to have one too under the GFA - is a balanced vote (52%-48% for example), it will make divisions even worse. No Deal Brexit is very likely to bring forward the Reunification agenda prematurely, before there is, as there might otherwise be one day in the nearish future, a clear and unanswerable majority in NI for Reunification (or just as likely, had the UK continued as a Member State, the issue would just have faded away into nothing).
I appreciate that the problem with the border is that the EU cannot have an unregulated external border. Under the WA the whole point is that during the transition period there would have been enforced alignment and the UK would have continued to be able to trade as though it were still a member. In fact the much-maligned WA is rather a good deal for the UK: as for Corbyn's manufactured nonsense, claiming for example that it does not protect workers' rights, this is COMPLETELY UNTRUE. It specifically says that social and employment rights shall remain aligned, if one can be bothered to read the thing. Obviously the hordes of Labour moron backbench MPs could not be bothered.
NB for the sake of clarification, I am a Remainer, a socialist and was previously a Labour Party member (I resigned when Blair came to power).
The one glimmer of hope I have (I don't believe the MPs have enough time now to prevent No Deal, given Erskine May - parliamentary procedure - and the determination of the ERG, Cummings, etc.) is that the backstop could simply be renamed: Johnson calls it something else ("stopback"?) and it has the same characteristics as the existing backstop. But Johnson lies about this, claims it as a triumph, and the Brexiters - not the sharpest tools in the box - accept this. The DUPs might kick up a stink but enough Labour MPs might just vote for it. The EU27 would have to accept this Orwellian renaming. They might or might not be prepared to accept this for the great prize of avoiding No Deal and the terrible breaching of the GFA.
* "other arrangements" - this is an allusion to the very singular geographical, social and economic relationship between Ireland and the UK: the Republic of Ireland has no other land borders, and very very tight connections with the UK economy. It might make sense, as part of a way of avoiding a hard border, to incorporate aspects of a border, on a time-limited basis, between the Republic and the remainder of the EU27 as part of a comprehensive, complicated, partly technological solution designed to preserve the GFA. The transition period would give quite a bit of time to delve into all these aspects on a basis of mutual respect. But no... it is not to be.