The question isn't about the principle. As I've mentioned here before, personally I'm against it on democratic grounds. (Yes, the Leave campaign lied, but then so did the Remain campaign - remember George Osborne's emergency budget? Nick Clegg lied about tuition fees, David Cameron lied about being green and not mucking around with the school system, Tony Blair lied about - well, take your pick. That didn't make their governments unconstitutional.)
No, my question is about procedure. As I understand it, the idea is that the British people should be given a vote on whether they accept the terms that have been negotiated for Brexit by the Government. But substantive negotiations won't even begin until after Article 50 has been triggered, and once that has happened there's no way (as I understand it) to untrigger it. The clock is ticking inexorably down an exit two years later.
Of course, it might be that the rest of the EU would be willing to have the UK back and to waive Article 50, but it would be under no obligation to do so on the same terms, surely, with the whole panoply of opt-outs and rebates that the UK has enjoyed until now? Would a UK that changed its mind be allowed to stay out of the Euro, for example? Or wouldn't it more resemble that moment in The Merchant of Venice, when Shylock realises he's not going to get away with taking his pound of flesh:
SHYLOCK: Give me my principal, and let me go.
PORTIA: He hath refused it in the open court:
He shall have merely justice and his bond.
In short, aren't people calling for a post-negotiation second referendum misunderstanding the legal position entirely? Or is that me?