The reason the abduction theory does not make much sense is that the McCanns did not believe it was something that would happen. In interviews they have said things like 'it's so rare', 'it was the last thing on our minds'.
They did not consider abduction as a risk factor when they left the children in the apartment and every now and then listened outside for the sound of crying (which is what the nannies used to do in some resorts when parents ate their dinner - they would listen outside the bedroom doors of the sleeping children.) The reason for their listening outside was to hear if any of the children were crying.
Given that abduction by a stranger was something they considered to be very unlikely, why would it be the fist conclusion that they would jump to when Madeleine went missing?
There are a score of other things that could have happened. She could have been hiding somewhere in the apartment (for instance she woke up and was scared and hid somewhere). She could have sleep walked either to a hidden corner in the apartment or indeed somewhere outside the apartment. She could have gone off to try to find her parents - to the creche, to the restaurant and so on.
She could have tried to get to one of the other apartments where the McCann friends' children were asleep - in other words trying to find one of her friends. Someone could have heard her crying, or heard an accident and gone into the apartment to comfort her. If there had been an accident while the children were unattended someone could have taken the child to the creche or to get medical help. A nanny could have gone in, heard her in distress and taken her out to find her parents or to the creche.
She could have wandered around the resort and got lost, or wandered out of the resort. A kindly person could have found her and taken her somewhere to try to locate her parents/the police.
And so on and so on.
But no - the parents who did not believe that their children were at risk from abduction by a stranger were practically from the outset convinced that their child had been abducted - and abducted by someone working as part of a paedophile gang.
That to me does not make sense.
And as I have repeatedly stated, the last people who saw Madeleine are crucial to any investigation into a missing child.