For urban politicians, gun control is like the bar in "Cheers"—a place of refuge they can seek out whenever things aren't going well. Things aren't going well on the crime front in Chicago, with homicides up 25 percent this year. So what else can our elected leaders do but promise action against guns?

Action against the possession and use of guns by violent felons would be a good idea, but the proposal offered by Cook County Board President Toni Preckwinkle is something else: a penalty on nonviolent citizens who bear no blame for the carnage.

Preckwinkle suggested a tax on sales of firearms and ammunition, with the goal of defraying the costs that gunshots create for the county hospital and jail. Her spokesperson couldn't say what the tax rate would be or how much revenue it would yield but said the fee would be "consistent with our commitment to pursuing violence reduction in the city and in the county."

It won the support of Chicago Mayor Rahm Emanuel, who reiterated his commitment to "get guns and drugs off the streets"—as though this tax would dry up the existing stockpile of guns or reduce the flow of new ones.

The levy was dubbed a "violence tax," which is exactly what it isn't. It would not target criminals who have malice in mind, but would fall entirely on the law-abiding.

Anyone convicted of a felony, after all, is ineligible for an Illinois Firearm Owner's Card, which is legally required to buy guns or bullets. Under federal law, felons are barred from owning guns. So ex-con gang members would not pay the tax, because they make all their purchases in the illegal market. It would hit only those gun owners who have used their firearms responsibly.

Preckwinkle apparently regards her measure as the equivalent of taxes on tobacco or gasoline, which attempt to recoup from smokers and motorists some of the expenses they create for the medical system (when they get emphysema or lung cancer) or the road system (when they drive). But it's a false parallel.

The great majority of gun owners never cause the county to spend money providing medical care to gunshot victims, and they never take up expensive lodging in the county jail. Their guns don't impose a cost on society any more than a softball team's bats do.

The notion of taxing ammunition may be traced to comedian Chris Rock, who once quipped, "If a bullet costs $5,000, there'd be no more innocent bystanders." Before that, the legendary New York Democratic Sen. Daniel Patrick Moynihan suggested a 10,000 percent tax on the most destructive bullets. Make them too expensive, he theorized, and they would disappear.

Oh? Marijuana and cocaine are more expensive than they would be if they were legal, yet there is plenty of supply as well as demand. Put an extravagant—or even not so extravagant—fee on bullets, and black-market entrepreneurs will make and sell them outside regulated channels.

Active criminals have a strong interest in arming themselves, which is why even total bans (as Chicago long applied to handguns, until the Supreme Court interfered) don't have much effect on them. When your livelihood requires a deadly weapon, you will find a way to get it.

It's not as though criminals need a daily supply of ammo, making the tax a prohibitive expense. Legend has it that gangster Al Capone said you can get more with a smile and a gun than with just a smile, but he didn't usually need to pull a trigger to induce cooperation.

Even peaceable citizens are not likely to make a habit of paying the tax, since it invites widespread evasion. Anyone who wants to buy a weapon or ammunition can travel to a neighboring county, where gun retailers are more common anyway.

A county can do well with heavy duties on beer and cigarettes because people consume them often and want easy access. But a firearm purchase is not a frequent event in the life of a gun owner. Most hunters and target shooters won't mind an occasional suburban trip to pick up a few months' supply of ammo.

In the end, criminals will never pay the tax, law-abiding citizens will rarely pay it, and the county will get little revenue. The only purpose it will serve is to let upstanding gun owners know their local government views them with disdain. The feeling, for good reason, is mutual.