I think most people don't view social networks as extracting value from their user's the way they view financial traders doing so.

Some people will say that quant trading adds some value, but that the amounts the traders reap is too much.

I believe the value quant trading provides to its customers in proportion to the value it extracts is on par with social networking. A lot of the people who make arguments that quant trading provides no value have no idea how to value the liquidity that quant traders provide in the same way they can value what social networking provides. To appreciate what (most) quant trading firms provide, you have to have transacted frequently and significantly in the market.