Joe “the Plumber” Wurzelbacher did himself (and gun advocates) no favors when he wrote “your dead kids don’t trump my constitutional rights.”

He posted those incendiary words soon after Elliot Rodger went on a killing rampage in California, killing six people, three with a knife and three with a gun. In the weeks since, there has been more gun violence, most recently in Oregon.

To be fair, Wurzelbacher’s letter — directed to the parents of the gunshot victims — was replete with expressions of sympathy; but those civilities were undermined by his indelicate and insensitive harangue against Richard Martinez, whose son was among the murdered. Martinez had attacked “craven, irresponsible politicians” and the National Rifle Association for his son’s death.

Not surprisingly, the media have focused on Wurzelbacher’s rabble-rousing dictum that public safety — even if kids are mowed down by guns — is subordinate to Second Amendment rights. What should we make of that claim? Is there a kernel of truth in defense of Joe the Plumber?

Let’s start with this proposition: Constitutionally guaranteed rights are not absolute. For example, the First Amendment instructs that government “shall make no law … abridging the freedom of speech.” Yet we have laws that prevent incitement to riot, lying in commercial ads, and defamation, among other abridgments.

Similarly, when the Second Amendment directs that “the right … to keep and bear Arms shall not be infringed,” it does not ensure that a deranged person can possess a machine gun in a schoolroom. Some people, some weapons and some circumstances can be regulated. The Constitution does not preempt common sense.

On the other hand, the Supreme Court declared in District of Columbia v. Heller (I was co-counsel to Mr. Heller) that the right to bear arms is “fundamental.” That means individuals enjoy a presumption of liberty and government bears a heavy burden to vindicate regulations that compromise core Second Amendment freedoms. The burden-of-proof point is critical.

Even Judge Richard Posner, who had been highly critical of the Heller decision, wrote in an Illinois case that:

“a right to carry firearms in public may promote self-defense. Illinois had to provide us with more than merely a rational basis for believing that its uniquely sweeping ban is justified by an increase in public safety. It has failed to meet this burden.”

Ditto for the latest calls from several senators for more gun control legislation — expanded background checks, a waiting period, one-gun-per-month purchase limits, a ban on “assault weapons,” and no large capacity magazines. Those proposals cannot be linked to the Santa Barbara murders. The senators plainly have not met their burden.

California’s gun laws are among the nation’s most restrictive. The state has already enacted expanded background checks, which Rodger passed because he had no criminal or psychiatric record. The state already bans so-called assault weapons. Rodger’s three handguns had none of the specified features. The state already limits magazines to 10 rounds. Rodger had more than 40 qualifying magazines. The state already caps handgun purchases at one per month and requires a 10-day waiting period; but Rodger, who planned his massacre over nearly three years, had plenty of time to build an arsenal.

There are good reasons for politicians to resist nationwide gun controls that demonstrably do not work. And there are good reasons to suspect that the mass murder problem can best be addressed by improved detection and treatment of mental illness. And yes, the NRA has supported background checks that forestall buyers who have been involuntarily committed to mental institutions or judged mentally incompetent.

So, in those specific respects, Joe the Plumber has a point. He obviously needs a lesson in decorum; his absolutist message cries out for subtlety; but the principle that government must prove its case before trumping constitutional rights is perfectly valid.