Definitely very valid points.

And if we stop thinking about the McCann parents the way we imagine them to be, like our good selves, then we begin to realize that perhaps they WERE different.

Perhaps the parents were selfish and cared more about their entertainment in their lives and perhaps the children were considered second to the parents lives, inconvenient and a nuisance even.

We only see a small glimpse of the parents through media, and it's possible they are putting their best foot forward when eyes are on them. 

Lets not forget they may be the best parents, totally innocent and perhaps it was the first time the children had been left alone and Maddie was abducted, BUT one cannot forget the fact that such young'uns were left alone. There lies the cause and problem.