It's the specificness of it. Much like Kate's 'couple' when talking to Yvonne Martin.
Do you believe that every word Kate spoke to Yvonne Martin was related back by her to the police? Not a chance. Once again we do not know the whole conversation or the context in which things were said. Thinking her daughter may have been taken by people who wanted a child is just one of the possibilities which would go through Kate's mind at that time - what is wrong with that?
You seem to think that it is only the words recalled by YM that were actually spoken by Kate during that 'meeting' This is plainly nonsense. Whole loads of stuff will have been left out. People are not tape recorders.
Just as nonsensical as believing that the only people who saw Madeleine on the 3rd were the people who have made statements mentioning that fact. Loads of other people may have seen her - they just haven't felt the need to come forward to tell anyone - as it has never been in question. And yet IIRC there are people who claim that she died before the 3rd May - on the grounds that there is only one independent witness who saw her alive on the 3rd - and she has been bribed.
Where is their common sense?