It's this simple.
The first referendum question: 'Should the United Kingdom remain a member of the European Union or leave the European Union?'
The answer comes back No.
All fine. Go through parliament, get approval for Article 50 to start the process to leave (which will pass through as parliament will accept the democratic principle of the referendum).
At that point, we're negotiating the terms of leaving. We have NOT been asked what terms we leave on - neither parliament or a referendum has had a chance to judge those terms.
Therefore, the second referendum makes perfect sense - not to ask again if we should leave, but the question should be.
"Do you support the process of leaving the European Union via the Brexit Act 2018 (or whatever it'll be called)?"
At that point, we should actually have referendum after referendum until the answer is Yes, because Article 50 can be cancelled at any point in those two years, so if we keep getting the answer No at that point, there's no reason not to re-run (it'd be ludicrous if it was an unimportant issue, but this is the biggest issue of a generation - it makes sense to do it thoroughly).
But during the process, if we keep getting No and it's looking likely the public have changed their mind for economic reasons or whatever, then we should ask the original question again.
People who have applauded the referendum have applauded democracy in action - therefore, why are you all so scared of democracy continuing to act? You trusted and applauded the public for its' decision in the first instance; why be so wary of asking them again about the terms? Or, if you really are afraid of another referendum, why not advocate parliament having a free vote on it according to their conscience, given they are elected to govern?