FACEBOOK. Instagram. Google. Twitter. All services we rely on — and all services we believe we don’t have to pay for. Not with cash, anyway. But ad-financed Internet platforms aren’t free, and the price they extract in terms of privacy and control is getting only costlier.

A recent Pew Research Center poll shows that 93 percent of the public believes that “being in control of who can get information about them is important,” and yet the amount of information we generate online has exploded and we seldom know where it all goes.

Facebook and other social networking sites that collect vast amounts of user data are financed by ads. Just this week Instagram, which is owned by Facebook, announced plans to open users’ feeds to more advertisers. The dirty secret of this business model is that Internet ads aren’t worth much. Ask Ethan Zuckerman, who in the 1990s helped found Tripod.com, one of the web’s earliest ad-financed sites with user-generated content. He even helped invent the pop-up ad because corporations were wary of the user content appearing next to their ads. He came to regret both: the pop-up and the ad-financed business model. The former is annoying but it’s the latter that is helping destroy the fabric of a rich, pluralistic Internet.

Mr. Zuckerman points out that Facebook makes about 20 cents per user per month in profit. This is a pitiful sum, especially since the average user spends an impressive 20 hours on Facebook every month, according to the company. This paltry profit margin drives the business model: Internet ads are basically worthless unless they are hyper-targeted based on tracking and extensive profiling of users. This is a bad bargain, especially since two-thirds of American adults don’t want ads that target them based on that tracking and analysis of personal behavior.