You might blame this — in part — on robots. According to the research firm eMarketer, American companies are now spending more than $22 billion a year on “programmatic ads,” the kind of advertising that is bought with little human oversight. Joshua Zeitz, vice president of corporate communications at the ad-tech company AppNexus, explained to me how this automated ad buying works. When you click on a link, “in less than a second, a call goes out, and algorithms and automated software bid in an auction to put their advertisement up on your page,” he said. “So maybe the Nabisco algorithm wants to put an ad up there; so does Macy’s and so does Honda.” The algorithm that places the highest bid wins the chance to appear on your screen.

Programmatic ads can also follow individuals around the internet, based on their browsing history, as happened with Mr. Philips. A single targeted ad could cost just a fraction of a penny, but the pennies add up to a billion-dollar industry.

Even when ad placements are automated, companies still have the power to control whether neo-Nazis or fake news hucksters profit. In fact, it’s actually rather simple for companies to impose ethical policies, according to Mr. Zeitz. Indeed, his own company (which handles programmatic advertising for other organizations) recently decided to get out ahead of the issue by removing Breitbart News from its advertising marketplace. “We’re not banning them because they’re alt-right or conservative. We banned them from our marketplace because they violate our hate speech policy, which prohibits ad serving on sites that incite violence and discrimination against minority groups.” (Breitbart has said that it condemns racism and bigotry “in any form.”)

He pointed out that brand-name companies had already figured out how to keep their ads from flowing onto porn sites, because “you really don’t want your ad for a breakfast cereal next to a hard-core pornographic video,” and so “there are tools in place that allow companies to control where their ads go.” A company can block a specific site like Breitbart News from its ad buy. Or it might pick a “white list” of sites that align with its values.

But to do that, companies would have to forgo the sites designed to deliver exactly what they want — a big audience for little cost. In November, NPR reporters interviewed Jestin Coler about his fake-news empire. Mr. Coler and his team stage-crafted their sites to look like local newspapers and then planted fantastical headlines and fictional stories that attracted more than a million views. Though the news was fake, the ads were real. Mr. Coler wouldn’t tell the reporters exactly how much he made off advertising, but he intimated that his revenues ranged between $10,000 and $30,000 a month.

Such “entrepreneurs” have an outsize influence on our political sphere. BuzzFeed News reported that, during the last three months of the election, hoax stories outperformed real ones on social media. Thanks to people enthusiastically sharing pro-Trump headlines cooked up by clickbait farms, in the bizarro-world of online advertising, the fake can be more profitable than the real.

Ezra Englebardt, an advertising strategist, joined the Sleeping Giants campaign because he believes it creates much-needed transparency in the online advertising world. When lots of people share photos of the ads that they’re seeing on their own screens, it becomes possible to get some sense of where the ad dollars go, he said.