Time and time again we see arguments here about what did or did not happen.
Most of these arguments rely on assumptions about what evidence there is for any possibility. Those that strongly believe the McCanns to have been more involved in the case than leaving the children alone need to build a water tight case that would convince people (whether neutral observers, the public, or the judicial system. This is a massive wall to climb.
People who doubt the McCanns were so involved need do no more than point out the myriad possibilities that could have caused the disappearance of Madeleine; they do not have to prove anything.
One of the biggest myths built up falsely by the McCann doubters was 'Abduction is impossible'. This is chanted regularly and on some fora is a shibboleth- if you do not believe it, you are banned. Yet it is logically impossible to prove such a negative, and no attempt to do so is ever going to be successful because whatever the circumstances whilst the full story is unknown, any outcome remains possible, even if against the flow of evidence. This is the problem of induction. The case of the Black Swans shows this to be true and induction to be incomplete.
Because people who tend to believe the McCanns to be innocent (or hold it to be the case as a matter of justice) have so little to do to uphold their position, people who accuse the McCanns feel as if those that do not are in some way cheating. They do not realise that it is not a level playing field, but a large mountain to climb if they are to have their case accepted as being near the truth.