Montgomery County, Maryland is the latest locality to impose a 5-cent tax on shoppers or restaurant-goers who need a plastic bag to take their purchases home.  Next door, Washington, D.C. imposed such a tax already; environmentalists are pushing localities everywhere to do the same.

The tax is insignificant as a revenue-raiser -- perhaps $1 million a year will be collected, and probably less.  The tax is in fact designed not to be collected.  Relative to the actual price of producing such a bag -- not even 1 penny -- the tax is outrageous, at a 400-percent rate.  Few people will pay 5 cents for something they value at zero -- they will go to significant extremes to avoid it, even if it adds "only" 25-50 cents' added costs per trip to the supermarket.

Defenders of the tax say this is exactly the point.  They happily gloat that this is a tax which results in a change in behavior that they have long wanted to see.  Suffice it to say, it is nice that liberals occasionally acknowledge that taxing something produces less of it.

But that intellectual victory for conservative principles of taxation is probably a one-off.  This is not an ordinary public policy discussion.

Let's take the tax's defenders at their word that their real goal is to eliminate the unsightly waste of loose plastic bags floating in streams and in traffic medians.  But there are other forms of trash often found in streams and traffic medians.  Beverage containers.  Fast food cartons.  Political yard signs.  Shall we tax people at a rate of 400 percent merely to possess these items?

We do tax items to capture their "cost" to society.  We tax gasoline.  We tax cigarettes.  The only way you can justify such a penalizing tax rate on a product is if you can say that whatever utility it serves, its external negative features -- the problems it causes -- are so large that the product itself is profoundly dangerous to life, liberty, and the Republic.

Are plastic bags that awful?  Their production, we are told, involves chemicals and plastic compounds that poison our air and water for eons.  Sounds bad.

But plastic bags are terrific devices.  They are feather-light, yet hold several pounds of goods.  They can be reused multiple times.  Dog-owners are grateful to have them for some disposable protection when they pick up after their pets.  Parents of newborns are thrilled to encase a particularly nasty diaper on the fly.

Compared to these benefits, how awful is the environmental damage plastic bags are alleged to cause?  We cause far more environmental damage for far less practical benefit.  There are other pollutants of our streams -- pesticides, fertilizers, and old tires, for example -- but we don't impose 400-percent taxes on them.

No, the only obvious reason to impose such a tax is that it is purely symbolic.  Those who hate plastic bags hate them so much that they also hate the people who use plastic bags.  A 400-percent tax on something is passed not to capture the external negativities of a product.  It is imposed to punish the person who might ever want the product.

Of all the things that supposedly imperil society -- cop-killing bullets, unsecured nuclear waste, deadbeat dads, gas-guzzling SUVs, factory farming, just pick your poison -- plastic bags alone are targeted for punishing tax rates and, it is hoped, disappearance.

Is that because plastic bags are worse than the other evils?  No.  It's because the use of plastic bags at the store is considered a moral evil by the nags of the retro-puritanical environmental movement.  When they can't change behavior through gentle or annoying suasion, they turn to the powers of the state.  So they have resorted to the equivalent of blue laws -- a state-imposed ban on otherwise harmless behavior to satisfy the moral urgings of a powerful political bloc.

Blue laws are a form of publicly sponsored religion.  Why aren't liquor stores open on Sunday in some places?  Because someone judged that it's not moral for the state to allow liquor sales on the Christian Sabbath.  There is no practical benefit whatsoever to the law.  But to those of a certain faith, it's just the way things should be.

The bag tax functions as a blue law: a way to impose one's definition of moral behavior.  I am a religious man, and I recognize state-compelled faith when I see it: the 5-cent bag tax has all the articles of a religious edict, sponsored by the state.

This isn't a tax.  It's an act of self-stroking for those who use reusable shopping bags.  Who can blame them?  All those years of lugging their smelly and sticky reusable bags from their cars through the supermarket and back, while the rest of us freeloaders were happily double-bagging our milk.  How frustrating that must have been!  Well, here's their revenge, I suppose.  A 400-percent tax on a piece of plastic that starts its life holding oranges and ends its life holding dog poop.  If this is a victory for public policy, our Republic is in greater danger than I thought.

Noam Neusner, a communications consultant with 30 Point Strategies, is a former speechwriter for President George W. Bush.