My boss shared a story about his time at Facebook. He was working on ads during 2012 election, and Facebook had a problem. It was just a couple of weeks before the election and the Romney campaign had money to burn. They were winning auctions on facebook left and right. The problem was that too many people had clicked the "never show ads from this source again" button on the ads. Guess what, he was tasked with turning the button off for Romney ads, now facebook could show as many political ads as the campaign could buy.