Of the following, Robert Jones is sure: President Barack Obama is attempting to flood the United States with immigrants from south of the border who will vote Democrat – and in the process, a veritable smorgasbord of terror groups will also slip through the loosely guarded border, unleashing chaos.

This is why Mr. Jones needs his guns.

"That's a reason to have these, right there," the grandfather, historian and ordained Presbyterian elder says, pointing to a handgun and a rifle on his kitchen table. "Because of ISIS, al-Shabab, Boko Haram – you pick."

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Mr. Jones is a resident of one of the most gun-friendly cities in the United States – Kennesaw, Ga.

Not only is gun ownership encouraged in this quiet Atlanta suburb of 32,000, it's technically mandatory. For more than three decades, Kennesaw has had on the books a law requiring every household to have a weapon.

In truth, it's unenforceable. But the very fact that the law exists – and still enjoys widespread support here – illustrates the immense divide over guns and gun control that still dominates politics at the state and national level. Kennesaw's mandatory gun-ownership bill was conceived as a direct response to another town's gun prohibition law. That makes it one of the clearest examples of the theme that runs through the bitter U.S. gun debate: that the Second Amendment of the U.S. constitution, which enshrines the right to bear arms, is an all or nothing proposition.

Kennesaw adopted its law in response to a 1981 decision by the Chicago suburb of Morton Grove to make gun possession illegal within village limits. (The ban was challenged in court, unsuccessfully, although the village dropped the law in 2008.)

Kennesaw, according to people here, saw red. To hear the town's residents tell it, the news of Morton Grove's law was doubly annoying. Not only did many here believe the village had trampled all over the Second Amendment, but the press all over the country jumped on the story.

"If the mainstream media hadn't given that so much positive play, Kennesaw never would have passed the law," says Mr. Jones. "I mean literally in Kennesaw they wanted to get it off the front page of the newspaper."

And so Kennesaw passed its own law requiring every household to have a gun. As anything other than a rhetorical symbol, the law was toothless – it contained exemptions for anyone who couldn't afford a gun, had a mental or physical health issue, or simply didn't want to own a weapon. Nobody here has ever been arrested for not owning a firearm.

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And yet it achieved its central purpose: It made a statement on behalf of all those who believed that the laws in places like Morton Grove were initial steps in a nationwide effort by liberals to take away gun-ownership rights entirely. It fit perfectly the narrative in which gun owners are cast as endlessly persecuted at the hands of an overreaching government.

"I rejoiced" when the Kennesaw law was passed, says Dent Myers, the 84-year-old owner of Wildman's Civil War Surplus and Herb Shop in the heart of the city, a store specializing in rare (and often plainly racist) Southern collectibles."It shows that we're exercising our Second Amendment rights, and most of our rights have been taken away.

"It was a rebuttal to Moron Grove – I call it Moron Grove."

With the exception of characters such as Mr. Myers, who constantly carries holstered handguns on both hips, there are few signs that Kennesaw might be the most pro-gun city in America. There are billboards on the outskirts of town advertising myriad gun stores, as well as Airsoft replica gun store advertising Special Forces-style simulations to children under the tag line: "Fake Guns. Real Fun."

"The majority of adults in the area are probably gun owners because there are so may sportsmen and people who hunt," says Lieutenant Craig Graydon of the Kennesaw police department. "But it's not something that's a topic of conversation every day. You usually don't see people walking down the street talking to each other about their guns."

Lt. Graydon does say, though, that in the year after the law went into effect, serious crimes in Kennesaw dropped significantly, and have remained low over the following decades, even as the city grew from a small rural community to a sizable Atlanta suburb. He attributes that largely to good policing and local government efforts, not just the law.

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A flood of lawsuits from pro-gun and anti-gun groups in recent years have made laws such as those of Kennesaw and Morton Grove much more difficult to pass. In 2013, the tiny town of Nelson, Ga., tried to pass a motion similar to the one in Kennesaw. However the Brady Center, a gun-control advocacy group, sued the town. As a result, Nelson amended the law to explicitly say that residents also have the right not to bear arms. On the other end of the spectrum, the National Rifle Association fought (and won) a bitter legal battle to kill Chicago's attempt to ban gun stores in the city, after the Supreme Court struck down a city-wide gun ban.

"It's one of those things that, if you tried to pass it today, I think it would be challenged," says Kennesaw Mayor Mark Mathews. "Because we've created an environment where … government is not there to push a position one way or another, and any time they try to do that I think it gets challenged – and rightfully so, to a certain degree."

Indeed, at the federal level the all-or-nothing political battle is at a draw. President Obama has been unable to get gun-control measures through Congress. A recent attempt by the Bureau of Alcohol, Tobacco, Firearms and Explosives to ban a certain class of bullets was withdrawn after countless outraged letters from pro-gun advocates. But bills have been introduced in the Republican-controlled Congress to scale back gun-control laws in the District of Columbia and to allow anyone with a concealed-carry permit in one state to have a concealed weapon in any other state that issues such licences.

At the state and local level, gun advocates have made inroads using the same arguments that were made in Kennesaw – that it's necessary to normalize and expand gun use in the face of perceived encroachment on the Second Amendment. Kansas legislators passed a law this month allowing residents to carry concealed weapons without a permit or having to undergo a previously mandated training session. Ohio is considering a similar measure.

In his suburban family home, Mr. Jones says that when people ask him why he needs his three guns (on this day, his wife has taken the third weapon; she's out with the grandchildren), he says self defence.

"They say, well, who do you need protection from? And my response … is to protect myself from liberals like you who want to abrogate my constitutional rights.

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"They're always shocked when I say that, but I think if liberals had their way, if we didn't have Congress, they would take every private gun away."