@davidallengreen is of course right: if HMG reneges on the backstop it previously agreed this may well lead to a no deal Brexit, considerable economic damage to Member States including Ireland, and the very hard border the backstop was designed to avoid.
Does it follow that the EU was wrong to push the backstop? I don't think so. Avoiding a hard border was identified as one of the 3 key divorce issues and understandably so given the stakes. And HMG displayed bad faith on the issue throughout.
They clearly intended to use the Irish border issue to force the EU to accept no border controls anywhere, despite HMG being free to do trade deals with others, diverging in terms of regulations and all the rest of it. They were incredibly cynical.
David Davis said the Irish border would be a test case for borders more generally. Johnson said as much when he came to Dublin. And the 2 position papers in August 2017 also made it pretty clear that this was what was in their minds.
By that stage it was clear that HMG was negotiating in bad faith, and that is when the EU started becoming clearer in terms of spelling out what we basically all agree is required to avoid a hard border. What else was it supposed to do?
There was always going to be a crisis when the UK political system finally confronted the inescapable logic of borders and regulatory divergence. The problem is that it is now very late in the day and if HMG storms out of the talks or cannot deliver the Commons it may be too late
You could perhaps argue that the crisis should have been forced earlier. And in a sense it was, last December, but no sooner had HMG signed up to the backstop than Davis et al started arguing that it didn't matter. The EU pushed back hard then but should perhaps have been tougher