I can quite easily give an example of a deal that not even the most ardent Remainers would accept (but please let me know if you would!) E.g. The EU says we have to pay £100 billion up front plus £50 billion a year and accept free movement arbitered by the ECJ. And there must be a hard border in Ireland and our citizens living in the EU have no rights.
Alternatively I could foresee a deal involving minimum payments, restricted movement and reform of the EU guaranteed in advance. As a leaver I might well accept that.
All the forecasts of unmitigated doom, or perpetual sunlit uplands, are equally head in the clouds. At least let's have a reasonable discussion.