SACRAMENTO, CA - Quick guess, what is the biggest crop in the United States? Wheat? Corn? Oats? Nice try. Actually it’s lawn. It’s spring and many homeowners are out working on their lawn, which may soon bear the heavy bootprints of government. Consider, for example, developments north of the border.

There, the Sierra Club, World Wildlife Fund, and dozens of local activist groups are pushing to ban the “cosmetic” use of pesticides on private property. In other words, no use of weed killer on your own grass. And the activists’ motivation is not just personal. They invoke a measure that came out of the 1992 Rio Declaration on the Environment and Development.

It’s called the “Precautionary Principle,” but it would be a mistake to regard it as a common-sense measure based on “better safe than sorry.” There’s much more to it. Under the precautionary principle, the lack of full scientific certainty is no reason for postponing action to protect the environment. In other words, even if we don’t have the facts, the government should take drastic measures as a first resort. This approach carries risks of its own.

Power corrupts, and public officials always need careful monitoring, not more power. Further, public officials should pay more attention to science and less attention to discredited scaremongers. Consider Stanford’s Paul Ehrlich author of The Population Bomb (1968), a book that helped launch the modern environmental movement. Ehrlich, a bug expert, predicted that, because of pesticides, life expectancy in the United States would drop to 42 by 1980, when the U.S. population, he said, would be reduced to 22.6 million. Needless to say, the mass starvation and depletion of resources he predicted also failed to take place.

Likewise, the Alar scare, pushed by such great scientists as Meryl Streep, needlessly terrified millions of people. Likewise, electricity transmission and cellular phones do not, as some have charged, cause cancer. No principle can alter the hard reality that the world is a risky place. Living in proven earthquake zones such as Los Angeles and San Francisco, is risky. Driving on the Santa Monica Freeway during rush hour is risky, as is riding a bicycle on city streets and eating in certain fast-food restaurants. Lighting and heating our homes and disposing of wastes also entail risk. In a world of limitations, actual risks must take priority over potential risk.

A chilling effect on technology is another likely consequence of the precautionary principle. New technologies, including those that make for a cleaner environment, seldom appear overnight. They require extended research and development. But under the precautionary principle, they could be quashed if their first efforts do not achieve perfection. The principle could also halt the building of new bridges and high-speed rail lines that would reduce pollution.

Perfection is not attainable in public life or anywhere else. Therefore, sacrificing the good for the perfect, which the precautionary principle does, is no basis for public policy. Responsible public policy rejects fearmongering, realizes the inevitability of tradeoffs, and carefully considers the best science before taking action. That is why, at this point in history, policymakers need to reject the precautionary principle and consider instead a rule that usually applies to children: keep off the grass.