Whenever someone is hurt in an accident, people say, "There ought to be a law!" Politicians rush to oblige them and then take credit for all the lives they saved.

But shouldn't they also accept blame for the lives lost because of those laws?

Lives lost? Yes. A joint study by the Brookings Institution and American Enterprise Institute [http://www.aei-brookings.org/publications/abstract.php?pid=98] found that government regulations that are supposed to save lives actually end up killing more people.

Why? Because safety laws almost always have unintended bad consequences.

For years I've ridden my bike to work without a helmet, which seemed especially dumb since "20/20"'s offices are in New York City. I feel much safer now, but it's not clear that I am safer.

Ian Walker, a human-behavior researcher at the University of Bath in England, put a sensor and camera on his bike and rode for miles with and without a helmet. His data showed that when he wore the helmet, 23 percent more cars came within three feet of him.

"[The drivers are] saying,'He knows what he's doing.' When they see a cyclist who has all the gear, they think it's a sign of someone who's experienced and skillful," Walker surmises.

Biking is obviously less safe if cars are closer. Walker says there's another unintended consequence of helmet laws.

"Parts of Australia, Canada, and New Zealand have made bicycle helmets a requirement. The number of head injuries among cyclists in those countries drops off."

That's good, right?

"However, the number of cyclists is dropping off at exactly the same rate."

That's not good, assuming they don't take up other exercise.

"When people don't cycle, they're not getting exercise," Walker says. "Being sedentary is incredibly dangerous. You get heart attacks; you get strokes -- proven killers that kill thousands of people. So when people make helmets a requirement, with the best intentions, it may actually kill more people."

And here's another unintended consequence: Now that I wear a helmet, I feel safer, so I ride in traffic more often. Economists call this the Peltzman effect -- people adjust their behavior in ways that counteract the intended safety effect.

It's possible that I'd be safer if I junked the helmet and bought a woman's wig instead. Walker discovered that drivers gave him the most room when he wore a wig and they apparently thought he was a woman.

I tried it. It was very embarrassing, and I couldn't tell if cars came closer or not.

I'll stick with my helmet, but the point is that unintended consequences of well-intended safety rules are common.

In 1972, the FDA passed a law requiring child safety caps on many medications. It was supposed to keep kids from being poisoned by drugs like aspirin. But there is an unexpected side effect. Because safety caps are hard to get off, some people -- particularly older people -- leave them off, and some parents, feeling safer with the cap, leave the aspirin where kids can reach it.

A study of this "lulling effect" concluded that an additional 3,000 children have been poisoned by aspirin because of the regulation.

Finally, I may have given my daughter asthma by trying to protect her. When she was a baby, I, like most new parents, made an extra effort to keep the house clean. But now there's research suggesting that kids who are exposed to more endotoxins -- mild dust, bacteria, pollen -- and kids who go to daycare, have pets, and live on farms -- are less likely to develop allergies and asthma.

A sterile house, safety caps, bike helmet laws, etc., are all well intended, but one never knows what the real-life consequence will be. Yet every year the federal register needs thousands of pages to list all the new freedom-killing rules that bureaucrats pass in the name of protecting us.

Politicians should be less smug when they say, "Look, I've solved it! I passed a law."