Re: So predictable !
MPs aren't magicians. People want no freedom of movement, but also want a seamless border with NI/RoI and to have all of the benefits of being in the EU. This isn't possible, hence bickering as to which bit of the pipe dream should be thrown away.
The NI issue is a red herring. The UK government and people of Ireland don't want a hard border, the EU do. So, let the EU require Eire to institute a hard border with Northern Ireland, but the UK and Northern Irish government don't need to implement any such arrangements. It would be a one-way border control system. If the armed thugs choose to attack it, it won't be Northern Irish officials in the firing line.
In this scheme, the EU won't do any immigration or customs policing for the UK authorities, but there's already an open border despite different currencies, passports and tax systems, so the UK would be no differently off to how we are now. The people of Ireland would have to tolerate one way Eire border controls when crossing from Ni to Eire, but that's only as big a problem as the Dublin government choose to make it. If the locals don't like it, they would need to take that up with Dublin or Brussels.