When you get paid for your efforts that is the value that flows down the pyramid. An illegal pyramid has no value flowing down the pyramid. So if the company hired you and worked you, but didn't pay you, that would be an illegal pyramid. This greatly simplified example applies to churches, governments, and many other organizations. MUST have value flowing up and down the pyramid structure.
Money flows up the pyramid structure and product, services, training, and support flow down.
Therefore network marketing is as legal as IBM, Sony, your local church, or the US government. Network Marketing has been around for over 50 years. If Network Marketing was an illegal pyramid, and growing at this rate, it would have been outlawed years ago. Neither are ALL traditional type businesses. There are good and bad people in every industry and organization.