There's also the 'smart border' issue. At the start pro-Brexit politicians were saying the border issues can be resolved to a large or at least good enough ext

There's also the 'smart border' issue. At the start pro-Brexit politicians were saying the border issues can be resolved to a large or at least good enough extent with technology. Number plate recognition cameras, better IT systems, pre-registration, trusted trader schemes. A bunch of stuff together that'd mean no need for a hard border of the sort of that would set off the IRA blowing people up again. The EU dumped all over these ideas very publicly, laughed at them, described them as "unicorns", told the UK to get real etc. Two problems with that attitude: 1. It was a lie and they knew it was a lie. Barnier admitted it would work just a few months ago, after holding the position for years that it wouldn't. France just announced a very similar set of measures to handle the France/UK border. Borders experts had testified that the schemes were workable. The UK doesn't care if there's some leakage anyway so it doesn't even need perfection. 2. It has reinforced the idea in the UK and amongst the population that the EU is willing to go to any lengths to get what it wants. It has literally said to the UK: we insist that the price of leaving us is either terrorism and deaths, or annexation of large chunks of your territory. Entirely reasonable attempts at finding compromise were all rejected with insults and arrogance. This behaviour has not surprisingly infuriated many people, including many members of Parliament.