(FORTUNE Magazine) – For decades, the only thing anybody had to know about forest fires was that they were bad--and that Smokey the Bear wanted us to prevent them. Then naturalists began pointing out that the success of fire prevention efforts had left formerly wide-open Western forests choked with undergrowth and ailing trees. This wasn't just an aesthetic problem; all that added fuel meant that when fires did come, they were hotter, more devastating, and harder to put out than before.

It may be time to start thinking about financial crises this way. Ever since the Great Depression, currency crises and market panics have been seen as disasters to be averted at all costs. For 30 years after World War II, that meant regulating exchange rates and capital flows. After that system fell apart in the early 1970s, it was replaced with ad hoc efforts by the International Monetary Fund, the U.S. government, and other powers to put out financial fires all over the globe.

Now the role of the IMF has come into question, setting off a debate in Washington that, despite its many lapses into wonk jargon and nativist hoo-hah, really comes down to a pretty simple question: Are financial crises good, or are they bad?

Like forest fires, financial crises clear out a lot of underbrush. Badly run banks and reckless investors go under; survivors are reminded of the value of prudence. A market periodically tested by sharp downturns is less likely to develop the excesses that can lead to a truly devastating crash. These downturns, however, can wreak a lot of short-term havoc. Perfectly sound companies can be wiped out; diligent workers can lose their jobs. Even worse, the peculiar way banks traditionally work--they lend money for set periods of time but fund those loans with deposits that can be withdrawn at any moment--leads to liquidity crunches in which everybody wants his money back but nobody can get it. That, in turn, can lead to a real economic collapse.

Bank runs actually aren't the danger they used to be. Banks now fund their loans with commercial paper and CDs as well as with demand deposits, and the growth of international portfolio investment and direct investment has meant banks control an ever-shrinking share of the world's capital flows. The IMF and its allies, however, continue to preach the gospel that financial crises must be stopped. Part of this is due to an understandable fear of the unknown--no one can be absolutely certain that a bank run in Korea won't result in worldwide economic collapse. The other big concern is pure politics.

Consider what happened on the forest-fire front in 1988, when lightning sparked a few fires in Yellowstone National Park and park authorities let them run their natural course: Eight hundred thousand acres burned; the park was rendered unvisitable; houses were destroyed; and countless innocent critters were fried. On an ecological basis, the fires were a success--Yellowstone's plant and animal life is now thriving, and there's less risk of another huge, out-of-control fire. But the let-it-burn approach was a political disaster.

Similarly, the financial crises that hit several Asian economies last year probably could have worked themselves out without help from the IMF. But it would have meant complete surrender to the dictates of the global financial markets--the entire banking systems of South Korea and Thailand might have ended up in foreign hands. And if that turned out to be politically untenable in Korea or Thailand, well, then the crises might not have worked themselves out.

That's a real threat, and it means the IMF is not as useless as its critics contend. But it's not the same as saying the agency should douse every financial crisis it sees. Like the National Park Service and National Forest Service, which have backed off from their let-it-burn policies of the '80s but still argue that fire is a natural and healthy phenomenon, the IMF and its backers need to learn to appreciate a good crisis now and then.

--Justin Fox