It is very hard to actually sell the product (the content generated for Facebook or Google) for the people producing it. It has little to no value outside of the social network context that was provided. Thus, it seems to me more like the "sirens" are creating a market where no viable one existed before. There is no cost or value lost for the people using them. The value did not exist before the social network was created.

"There is no cost or value lost for the people using them."

That assumes the data isn't being used in a way that harms the interests of the user.