So how is a bad view of the McCann going to help anyone or anything?

What happened happened.  Not all children are at risk when they are left unwatched for a while.  All parents do it.  That's a normal part of life. It's not normal to assume that there is a child snatcher behind every door or wall.  There isn't.  That's why there are parks and paths and playgrounds and ice cream vans for children to run to alone - children freely move and grow when they have normal parents.  People leave the back door open, back gardens are open to the road or fields often - not all people live behind locked doors all the time.  It's the child snatcher that is at fault - not the Mc Canns.