Do you mind? It is not a different debate at all. The parents cannot be hung on the basis that they both murdered one of them (as Spam believes) AND neglected them to their fate at the hands of a paedophile. On second thoughts Spam probably can (and will) do both, illogical though it is. Also, it's worth pointing out that despite your apparent belief that the children were abandoned to their fate you also believe that there was scarcely a window of opportunity for an abductor to strike as members of the Tapas Group were in such close proximity to the apartment for most of the evening that it made abduction "virtually impossible" - so were the kids left to the mercy of an abductor or not?
That is where the phrase "small window of opportunity" comes into play. Especially if Madeleine got out the front door and a concerned person closed the front door from within. She could easily be taken by someone else off the street. We have no idea how many people were concerned by that stage of the week.
Mrs. Fenn, and the family above her, her niece, the staff at OC that Mrs. Fenn rang the next day, Silvia Batista, Jez Wilkins, and Bridget all seem to beware of the danger too. The staff at the Tapas restaurant too must IMO have known.
The presence of a couple of baby monitors on the table must have been a sure giveaway there were kids being left to their own devices.
Even the McCann friends were putting extra checks in at times during the week.