The traditional case against monopolies is that they are bad for consumers. But some technology companies, especially social-media concerns such as Facebook, complicate that, because they become more valuable to consumers the more they dominate the market. Facebook is like the telephone. One telephone user finds it not valuable at all — there’s nobody to call. Two telephone users find it of limited usefulness. A network of billions of users makes the telephone immeasurably more useful. Peter Thiel, founder of PayPal and an early investor in Facebook (who has written in these pages), says that he likes to invest in monopolies, but Amazon, Apple, Google, and Facebook are not monopolies in the traditional sense, leveraging their market power to squeeze more out of consumers via higher prices. They mainly do the opposite. “We measure an antitrust violation by looking at consumer harm — not harm to competitors,” Penn law professor Herbert Hovenkamp told PolitiFact. That’s one reason the Trump administration, in spite of the president’s big talk, probably won’t move against Amazon: There isn’t a case. When consumers begin to feel the bite, conventional economic theory goes, then competition will step in and set things right.

But what if the bite isn’t felt? We don’t write a check to Facebook or Google once a month. We compensate them in other ways — attention must be paid and privacy surrendered and personal data sliced and repackaged and traded like a subprime mortgage. The censors of the Catholic Church helpfully published the Index Librorum Prohibitorum, bringing some much-needed transparency to the process of suppressing thought: The list of banned books was plain as day. Amazon can just disappear a book if it so chooses or, if it’s in a devious mood, as it was during the Hachette dispute, it can monkey with prices, product placement, and delivery times to quietly hobble a work — or an idea. Many unreflective people cheered when the nation’s Web-hosting companies decided to dump a number of neo-Nazi websites, effectively removing their material from the online public square (which is the public square that matters). A lot of conservatives were a little queasy, though: The same people who support banning neo-Nazi communications also believe that everybody to the right of Hillary Rodham Clinton is a neo-Nazi, that criticism of transgender-rights efforts is “hate speech” that should be prohibited, that sermons endorsing the traditional view of marriage should be — and could be — a crime.