By contrast, Mike E. Peinovich grew up in liberal, affluent Maplewood, N.J. All you really need to know about Peinovich’s m.o. is that he hosts a podcast called “The Daily Shoah.” Peinovich’s father was so ashamed by his son’s radicalization that after the Charlottesville rally in 2017, he asked Peinovich to change his name — eliciting bruised complaints from Peinovich about his father’s abject insensitivity. “Perhaps if you had shown more sympathy and interest in fairness,” Mike Jr. wrote to Mike Sr., “my decision would be different.”

Is this a son who feels deeply hurt? Or is this a petulant man who has a preternatural gift for trolling? Could he be a bit of both — and does that mean anything? Marantz’s wife was once a public defender who represented some people accused of “horrifically violent” crimes; if you believe in rehabilitation, do you also hold out hope that even a few of the people Marantz meets might be redeemed?

Questions like these come up again and again for Marantz, who is an essential part of this narrative, which has as much to do with the collapsing media ecosystem that allowed these people to flourish as it does with the people themselves. Marantz knows that his subjects see him as a stand-in for an insipid media elite — a boring category that he bristles at, though the lurid extremism he encounters forces him to accept that he’s a “reluctant institutionalist.” He finds himself feeling protective of a system that he knows is flawed but is better than the cruelly nihilistic alternative.

“Of all that I resented about the Deplorables,” Marantz writes, “one of the things I found most irksome was that they forced me to think like an establishment shill.”

Marantz meets a number of women who joined the alt-right movement. Some of their stories exude a dismal obliviousness: A former Bernie Sanders supporter and ardent Bob Dylan fan — “one of the last true rebels,” she gushes — busily assembles gift baskets for the DeploraBall in Washington while the male organizers do nothing to help her, scrolling through Twitter on their phones. Other trajectories are downright chilling: One woman ascended the ranks of the alt-right by appearing “confident enough to keep up with the guys, but subservient enough to know her place”; she went from being a volunteer for the Obama campaign to someone who gave a Nazi salute.

As disturbing as these specific stories are, what filled me with a creeping sense of dread were the parts of “Antisocial” that incisively describe how a Darwinian information environment has degraded to the point where it now selects for people who can command the most attention with the fewest scruples. Marantz meets a 60-year-old “surly racist” with 25,000 subscribers on YouTube who, in another era, might have been relegated to muttering on his front porch.