Young people on both the right and left are also less wedded to political institutions. Those of us born in the 20th century had grown used to the idea that the right stands for tradition and the left for reform. In the liberal era, everyone was expected to hew quite closely to the status quo.

But what we see now is that both factions stand for revolution.

The conservative writer Rod Dreher recently asked a young man in Washington to outline the demands of his generation’s right-wing radicals. “They don’t have any,” he replied, “they just want to tear everything down.”

The Zoomer left is no less radical. In Harry Potter, the good guys do not deliberately kill, but instead stun or disarm their opponents. Here Ms. Rowling endorses a liberal commitment to nonviolence that appears to be falling out of favor, particularly on the left. In a recent YouGov poll, the respondents most likely to endorse the statement “political violence can sometimes be justified” skewed young and left wing. We saw a glimpse of this change in norms after the assassination of Charlie Kirk, when some young leftists responded with indifference bordering on glee.