Should automobiles be made as safe as possible? Most people might reflexively answer, "Certainly." But the indisputably correct answer is, "Certainly not."

Automobiles designed to sacrifice all values to that of safety would have a maximum speed of perhaps 15 miles per hour. They would be heavily reinforced in fuel-inefficient ways. They would have no radios or other possible distractions. And, by the way, if safety were society's sovereign goal, traffic laws would include a ban on (among many other things) left turns, which are risky.

Reasonable people do not talk about subordinating all values to any single value, be it safety, health, freedom, virtue, even justice. Fiat justitia ruat coelum(Let justice be done, though the heavens fall)? Heaven forbid. Falling heavens are costly. Balancing competing values is inevitable.

Which brings us to today's arsenic argument. Many people, uninterested in the pertinent science, denounce President Bush for overturning President Clinton's eleventh-hour regulation requiring the reduction of arsenic in drinking water from 50 parts per billion to 10 parts. Such people must believe, or want other people to believe, that water should be made "as safe as possible."

Are such people positive -- if so, how? -- that the health benefits of reaching that new standard would be worth the estimated cost of, for example, $400 million to New Mexico? How do such people know New Mexico could best use that $400 million that way rather than on more schools, courts, hospitals?

Bush's critics mostly misunderstand, or misrepresent, his decision, which is not to affirm the 50 parts per billion standard but to question the cost-benefit rationale of an 80 percent reduction. Often, as environmental standards increase in severity, health benefits increase minimally and costs increase exponentially.

And there are unanticipated consequences. Disregard the demagoguery about Bush's favoring "polluters" who "put" arsenic into water. Most of the arsenic in America's water is put there by nature. It is mostly in groundwater in rural, not industrial, areas. And in rural jurisdictions with small tax bases, the Clinton standard might have increased water costs so much that people would have dug their own wells, thereby increasing their exposure to arsenic.

One anticipatable, and desirable, consequence of Bush's presidency will be less moral exhibitionism (e.g., Clinton's arsenic regulation, which he evidently considered less-than-pressing business during seven years and 11 months of his administration) and more economic reasoning. For an introduction to such reasoning, try a new novel published, implausibly, by the MIT Press. "The Invisible Heart: An Economic Romance," by Russell Roberts, an economist, is the delightfully didactic story of a budding romance between two teachers at a Washington private secondary school -- he teaches economics, she English.

Instructing his class in the unintended consequences of government interventions in complex systems, the young economist tells his class about the elimination of wolves from Yellowstone in the first half of the 20th century. Wolves eat beavers, so beavers benefited, right? Not exactly. Wolves eat elk. Intensified grazing by the exploding elk population stripped vegetation from the banks of streams, including willow and aspen that beavers need for food. The beaver population plummeted.

In "The Invisible Heart" the young economist asks his class: There are 531 billion barrels of proven oil reserves, worldwide, and world consumption is 16.5 billion barrels annually, so when will all the oil be gone? Answer: Never. Why? Consider the Nut Room.

Suppose you love pistachio nuts, and are given a room filled with them to a level of five feet. But you must eat them in the room, and must leave the shells. When will you have eaten all the nuts? Never. As it becomes increasingly difficult to find nuts amid the shells, the nuts will not be free anymore. When the cost -- in time and effort -- of the nuts becomes too high, a substitute will be preferred -- nuts from a store, or another snack.

And before the most-costly-to-extract barrels of oil are found, we will switch to cheaper energy sources. Meanwhile, might it not be reasonable to extract the most accessible oil? Such as that in the Arctic National Wildlife Refuge? Do the costs of drilling there (in one-hundredth of 1 percent of the refuge, where there already are roads, airstrips, houses, military installations) really outweigh the costs of not drilling (higher energy costs, slower economic growth, increased national dependency)?

Political argument is becoming a puerile cartoon about the moral (e.g., environmentalists) doing battle with the immoral (e.g., "polluters"). This is a consequence of regarding a blithe indifference to the costs of moral exhibitionism as evidence of moral superiority.