* One of the most addictive products the world has ever seen (Opioids, another such product, were used to overthrow countries)
* The single most important media company in the world
* Controlled by one person
Threat to free society? Jury's out. But at this point, it certainly seems worth regulating.
(Edit: The above points are not meant to paint FB/Zuck in a bad light. To their credit, they've built an incredible ecosystem and a mind-bogglingly good product. We all strive to create sticky/addictive products.
My point is: When your product is incredibly addictive to a large chunk of humanity, regulation should be considered)