Haven't read this whole thread, but there was another thread a while back and Red Rose posted an article she'd written about the evidence that the McCanns' accidentally killed Madeline and covered it up, and I have to say that after reading that, as well as everything else, I agree that it's the most likely explanation.
I also think it's a little wrong that so much emphasis and money has been put to this case, and not to the billions of other missing people who disappear without trace and with not a second thought let alone a decade long news story. But I don't have any sort of bad feelings towards the McCanns', nor to their leaving of their children alone (yes, not a good idea, but their child is gone, punishment enough I think). If they killed her or she died and they covered it up, I don't believe that she was anything less than adored and I think that any following actions were the result of sheer panic, and it's clearly gone way too far if that is the case, but what can they do?! Tear their family apart yet further by admitting it and going to prison; allowing their younger children to believe their parents are monsters and their sister is dead? Seems simple to us, but who knows what could be going on for them both psychologically if in fact they know she's dead. Who knows, maybe they have led themselves to believe she really did just disappear.
And if they truly are ignorant then who on earth are we to criticise their actions, book included. We have no idea how we'd act or what we'd do and say if our child died or disappeared.