There seems to be a social convention that has formed around social media products that the user should never have to take out their credit card and actually pay. It makes sense why it started this way, since network effects are everything in this space.

But like many things that start one way for a good reason, that reason is eventually forgotten and the state of the world is codified into a shared social norm. Most people either don't care or are unfavorable to social media sites selling their info, yet I predict the outcry towards their charging would be enormous.