He didn't actually say that though, did he? What he said was that people should have the right to change their minds once the terms of Brexit become clear:

"I want to be explicit. Yes, the British people voted to leave Europe. And I agree the will of the people should prevail. I accept right now there is no widespread appetite to re-think. But the people voted without knowledge of the terms of Brexit. As these terms become clear, it is their right to change their mind."

Why are pro-Leave so concerned about either Parliament, or the electorate, or both, having a say on whether they want to accept the terms once they are clear? That would be another exercise in democracy, wouldn't it? Wouldn't that be "taking back control"? Does a proper democracy not allow for a change of mind? When did a political result become "in perpetuity"? that sounds more like a dictatorship than a democracy to me. The people have "spoken", yet you don't want them to have any opportunity for follow-up questions.

Could the concern be born out of the fact that once the deal becomes apparent, there might well be an awful lot less enthusiasm for it?

Once it becomes clear that there's no more money for the NHS, that net immigration will be little affected, that a lot of key workers will leave, that all the "red tape" that they complain about is actually either fictional or nothing to do with the EU (straight bananas, anyone?), that all those workers' rights they enjoy can be removed, will the electorate still be so keen on going ahead at that point?

The Tories and UKIP, now sadly with the collusion of a dysfunctional Labour, seem very keen that no-one, not even "the People" will get a chance to stop this, no matter how bad the deal is. And then you have to ask, why so keen on "Brexit at all costs"? Could it be because it fits very nicely into the Tory/UKIP ideal scenario for full privatisation and withdrawal of publicly-funded services?