"What would Jesus drive?" asks the new religious campaign against SUVs. Naturally, everyone has been eager to supply a punch line.

My initial thought was a donkey, which has considerably less passenger and cargo space than an SUV, along with emissions problems of its own. Then a colleague pointed out that Jesus was a carpenter, so he'd probably want a pickup truck, which falls into the same mileage and emissions category as an SUV, to haul his lumber.

On CNN's Talk Back Live, a guest suggested that Jesus might very well drive a big SUV, especially if he was traveling with the apostles. People interviewed on the street pictured Jesus in "a really, really, really long limo" (because "he'd have to travel in style"), a blue Miata ("economical and sporty"), and a Honda Civic (no particular reason offered).

One audience member said Jesus obviously would ride the bus, to be with "the masses." Another said he surely would walk, so the whole argument was stupid.

Taking the question literally is not just a way to poke fun at environmentalist puritans who cloak their ideological agenda in Scripture. It also reveals the fatuousness of the assertion that if you want to be a good Christian you should "drive the most fuel-efficient vehicle that truly meets your needs."

That's how the Rev. Jim Ball of the Evangelical Environmental Network summed up the message of his group's anti-SUV ads, which argue that God frowns on the Ford Explorer. But people generally do not buy a vehicle, which involves laying out or borrowing many thousands of dollars, for reasons they consider frivolous. They buy it because, in their judgment, it meets their needs. Truly.

People like SUVs because they're roomier, more comfortable, and safer than lighter, smaller cars. Although most SUV owners don't take them off road, they still value four-wheel drive in rainy or icy conditions. And yes, they like the way the cars look—i.e., a little more exciting than their fathers' station wagons. Is that a sin?

Apparently, it is. While Ball might allow that a big family or someone who often carries cargo truly needs an SUV or a minivan (which has a similar environmental profile), I suspect he would have nothing but contempt for the guy who commutes in a Jeep Cherokee because it looks cool.

Since I am not any sort of Christian, I suppose I have no hope of being a good one, but consider my situation as a thought experiment. I drive a 2000 Honda CR-V, which has a mileage rating of 22 mpg in the city, 25 on the highway. My wife drives a 2001 Toyota Echo, which has a 32/38 rating. Between the two of us, could we be at least a mediocre Christian?

Presumably Ball and his fellow anti-SUV crusaders hope to promote such debates in households across America. And if they manage to do that, they will accomplish—well, pretty much nothing, if their goal is to reduce pollution.

It's true that SUVs tend to get lower mileage and generate more emissions than other cars. But all cars and light trucks (including SUVs, pickups, and minivans) together account for only 1.5 percent of the world's man-made greenhouse gas emissions.

Looking just at motor vehicles, research by University of Denver chemist Donald Stedman has shown that 5 percent to 10 percent of cars are responsible for about half of tailpipe emissions. These "gross polluters" tend to be older, poorly maintained cars. If Ball and his allies really want to make a dent in car pollution, they should collect contributions to help people who can't afford to fix or replace these clunkers.

Instead, the anti-SUV crowd has focused on increasing fuel efficiency, both by encouraging drivers to choose cars with Jesus in mind and by pushing the federal government to raise mileage standards for light trucks—a move the Bush administration is considering. One problem with this approach is that higher fuel efficiency makes cars cheaper to operate, which encourages people to drive more.

Another problem is that making cars more fuel efficient often means making them lighter, and therefore less safe in crashes. A 1989 study by researchers at Harvard and the Brookings Institution concluded that fuel economy standards kill thousands of Americans each year.

Getting people out of SUVs and into lighter vehicles means some of them will die in crashes they otherwise might have survived. What would Jesus say about that?