MAYOR KENNEY wants to impose a hefty tax on soda and sugary drinks and use the revenue to pay for universal preschool for the city's 3- and 4-year-olds. It's a bad idea, for a lot of different reasons.

Kenney insists his proposal - unlike others tried around the country - is all about education, not about public health.

"The ancillary benefit to this will be healthy choices, but it's not the purpose," according to Kenney. "The purpose of imposing this 3-cents-an-ounce sugar-sweetened beverage tax is to allow people to get their kids educated and move them out of poverty into taxpaying citizens."

Odds are, the kids would rather drink the pop.

Despite Kenney's disavowal of any social engineering, the food nannies have come out in full force in favor of the proposal. Harvard public health researcher Steven Gortmaker says the tax would prevent 36,000 cases of obesity every year and save the lives of 730 Philadelphians over the next decade.

Kenney also is employing good, old economic envy, casting the battle as one between big, bad soda companies and darling, little toddlers.

The American Beverage Association has spent more than $3 million on a campaign against the tax, with an assist from a local coalition of small retailers, restaurant owners and the Teamsters (who drive the trucks that haul the soda). The tax, they argue, would cause shopping bills to soar and throw thousands of restaurant and grocery employees out of work.

The proposed 3-cents-an-ounce would be three times the rate in the only other city to impose such a tax, Berkeley, Calif. It would add $1.92 to the cost of a single 64-ounce drink, 36 cents to a can of soda, and $4.32 to a 12-pack.

Scott Drenkard, of the Tax Foundation, notes that the tax on a 12-pack of beer in Pennsylvania is only 9 cents. "So this proposal would be an excise tax 48 times larger than the current beer excise tax," he wrote.

The problems with Kenney's proposal are multiple and manifest. If it works, it fails. That is, if the tax works as a health measure and persuades people to drink less soda, less revenue will be generated and Philadelphia will have to go in search of something else to tax to pay for its shiny, new pre-school program. No one is trapped inside the walls of Philadelphia. People can leave the city to buy soda. And will.

Why only soda? Drinks aren't the only things people consume that contain sugar. Candy bars, Frosted Flakes, and that cake the state forced the Christian baker to make for the same-sex wedding, all have sugar in them.

It's regressive. Poor people drink more soda than rich people, and spend a greater proportion of their income on the drinks Kenney wants to tax. This might seem fair in the sense that they will also be the biggest beneficiaries of the preschool program, but that doesn't make the tax any less regressive.

Perhaps worst of all, the tax is a symptom of the larger disease of government nannyism and the dread fear among puritanical progressives - purgressives? - of the Ralph Nader variety that somebody, somewhere might be having a good time.

Sugar is bad for you. We get it.

We also like it. And potato chips. And steak. And bacon.

And some people don't. According to the Beverage Marketing Corp., sales of bottled water, tea and sports drinks are on the rise, while soda's share of the market has been declining for a decade. Beverage Digest reports that per-capita consumption of soda is at its lowest point in 30 years. Bottled water, already second on the list, is expected to move past soda in the next few years to become the most popular drink.

The soft sell has altered cultural norms, and the market has followed. There is no need for the heavy hand of government to impose a solution on a problem that doesn't exist.

For those of us who continue to imbibe, if we freely choose to partake of these abominations, we accept the risk, and that's really nobody's business but ours. The government should not be trying to change our behavior to suit the food fad of the day, or any other fad.

And if Philadelphia really wants to drop $400 million on preschool - on the dubious notion that such schooling makes much of a difference later on - that's the city's business. But it should find a more equitable, less regressive and less preachy way to pay for it.

John Bicknell is executive editor of Watchdog.org, a nonprofit journalism project of the Franklin Center for Government and Public Integrity.