To suspect that the family is responsible for the death of JonBenet you really have to accept that they were very skilled in some areas of cover-up. Particularly in calling as many people to the house as possible. This would be what the ransom and note were FOR. Without those two components, there would have been no avenue for immediately bringing as many people to the house to cross-contaminate the crime scene.
How could the Ramsey's have picked up the phone and called their friends and said "my daughter is missing, get over here" when those friends likely may have replied, "wouldn't you rather have me out looking for her somewhere?" No, that situation would have been ever more suspicious toward the Ramsey parents. So the ransom note had to happen. In order to get a bunch of people into the house two things had to be established: (1) JonBonet was missing and (2) taken with intention.
The media has greatly exaggerated the 118,000 dollars demanded by the note as too much of a coincidence, as that amount John had only recently received in bonus money. However, that too was a very clever play - if, indeed, the note was written by Patsy - because it only helped to give the appearance that the Ramsey's were constructively targeted, and another element within the ransom note to make the initial response about IT, about waiting for a phone call that is never going to happen, and not about the house, not about a body in the basement that has already been moved and, if all goes according to plan, will be moved again . . . right smack dab in the middle of all those people.