First, this is better for the parents (which in turn is better for the children) because there is usually more support readily available. Second, from an attachment theory point of view it is better if children are raised in a polymatric family rather than a monomatric family.
To go, where no man has gone before
It seems people like the whale sitter are the sign of a healthy society. A sign there are people in our society who will – Go where no man has gone before!