At the core of the Ponzi scheme is the central element, as an example, actually Ponzi or Sergei Mavrodi.  He attracts new members, money, organizes payments.  When the claims of payments are greater than the funds invested, the scheme falls apart.  This happens inevitably, sooner or later, since infinite expansion is impossible.  In the pyramids, each victim should become the leader of a cell and buy something from those who came earlier and sell those who came later.  If a really existing product is bought and sold, then it is legal, if just a license to sell licenses to the next victims, then it is illegal and also, sooner or later, collapses.