Your argument isn't sound. It doesn't matter who gives the rewards, what matters is the conditions under which the recipient receives the rewards.

> Thanks to Skinner's work, brain MRIs, and more recent research by psychologists, neuro-scientists, and behavioral economists, we now know how to design cue, activity, and reward systems to more effectively leverage our brain chemistry and program human behavior.

Effectively, Facebook designed a system that gives people rewards for giving people rewards.