All you needed to know about student activist David Hogg’s speech at the “March for Our Lives” in Washington, D.C., over the weekend was that he affixed a price tag on the microphone to symbolize how much National Rifle Association money Sen. Marco Rubio took for the lives of students in Florida.

The stunt wasn’t out of place. Indeed, it perfectly encapsulated the braying spirit of the student gun-control advocacy in the wake of the Parkland, Florida, school shooting.

These young activists are making our public debate even more poisonous and less civil, and are doing it as teenagers. They are precocious that way.

The Stoneman Douglas students experienced a horrific trauma. No one can deny their grief or blame them for being impassioned. And allowance has to be made for the fact that they are teenagers, who universally believe that they know better than their hapless elders (Hogg says the problem is that their parents don’t know how to use a democracy).

Yet none of that excuses their scurrilous smears of the other side in the gun debate. The student activists presume that there is a ready solution to mass shootings that everyone knows, and the only reason why someone might not act on this universally accepted policy is malice or corruption. This makes the other side the equivalent of murderers.

So at the CNN forum, Stoneman Douglas student Cameron Kasky told Sen. Marco Rubio that looking at him is like looking down the barrel of the AR-15 held by the school shooter.

In a video interview with an outfit called The Outline, David Hogg said that the NRA and its supporters “want to keep killing our children.” Not that they inadvertently enable people who carry out school shootings via misconceived policy, but they themselves kill children and want to keep doing it.

Lest he be misunderstood, Hogg added, “they could have blood from children spattered all over their faces and they wouldn’t take action because they will still see those dollar signs.”

This is the thought, if you can call it that, behind the price tag at the “March for Our Lives,” which Stoneman Douglas students also wore around their necks. It said “$1.05,” purportedly the amount of support Rubio has gotten from the NRA over his career, $3.3 million, divided by the 3.1 million public and private students in Florida.

In accusing their opponents of being bought off, the students deny the sincerity and legitimacy of supporters of gun rights. They treat the Second Amendment as an inkblot on the Constitution, and dismiss all counterarguments as transparent rationalizations. Not only is this a (appropriately) juvenile view of the gun debate that ignores Supreme Court jurisprudence, the genuine support of the NRA by millions of people and the serious, practical objections to gun-control proposals, it removes all possibility of a middle ground.

Tellingly, it is Marco Rubio who is the foremost object of the ire of the students, when he has been notably open and accommodating. He showed up at the CNN town hall to get abused, and has shown remarkable forbearance in handling political attacks on him that are shameless blood libels. He sponsored incremental school safety legislation that is becoming law, and for his trouble he is deemed a moral monster who doesn’t care how many people have to die as long as he gets a few more campaign contributions.

Maybe all of this can be written off as the work of overenthusiastic, underinformed 17-year-olds. But the student activists aren’t acting alone. They are promoted and praised by adults who should know better. Since the kids serve a useful purpose in promoting gun control, though, it is practically forbidden in much of the media to dissent from anything they say.

It was hard to believe that our public debate could get even more sophomoric. The student activists are here to say, Yes, it can.

Rich Lowry can be reached via e-mail: comments.lowry@nationalreview.com.