So this is where the immigration debate has taken us: to a 700-mile fence at the Mexican border, authorized in a bill passed by a panicked Congress, signed into law two weeks ago by President Bush.

The notion that throwing up a barrier will solve the problem of illegal immigration is fanciful. Even many who voted for the get-tough-at-the-border crowd has forgotten to consider how walling off the United States might affect Mexico's future — and how that will affect our future.

If the fence does succeed in drastically cutting illegal immigration — and given the determination of the migrants, this is hardly a given — we may discover that we've traded one problem for another set of problems that are far more acute.

Mexico has been rightly accused of exporting its social ills to the United States. In the 1980s, another of its periodic economic crises provoked a severe slump, and growth has been essentially stagnant ever since. With few jobs for the country's growing work force, many Mexicans headed north.

Net migration to the United States — between 25,000-50,000 a year through most of the 20th century — began rising rapidly. In the 1980s it hit nearly 250,000 a year and rose to about 500,000 a year in the '90s.

The money these workers send back is an important prop for the Mexican economy. If the door to opportunity is slammed shut, the risk of unrest on our southern border will increase dramatically.

Since the signing of the North American Free Trade Agreement in the early 1990s, Mexico has cut tariffs and privatized many state-run businesses. One-party rule has ended. The peso and inflation have been steady, and the middle class is growing, if slowly.

But the process of reform has moved at a glacial pace. In many sectors, business is starved for capital and growth is stunted by government rules that bar the foreign investment the country so badly needs. The transportation, electricity, oil, telecom and transportation sectors are dominated by government-protected monopolies.

The Mexican presidential election this year showed how deeply divided the country remains. The two leading candidates represented starkly different alternatives — the failed Mexican model of protectionist central planning vs. a vision of reform, competition and a breakup of monopoly privilege. The reform candidate, Felipe Calderon, won — but just barely.

If the fence is effective and blocks the route north, the already considerable pressures in Mexican society will increase and the fragile foundation of the new government will erode. We're fooling ourselves if we believe that with a mere fence, we can immunize ourselves if Mexico careens into yet another crisis.

The immigration debate in this country has failed to recognize that any stable, long-term solution is not possible unless it also takes the Mexican context into consideration.

Border security is part of that solution but so is a temporary worker program and a path to citizenship for those here already. And, of course, competent Mexican economic policies, so short in supply in the past, are critical.

Let's not forget that until the 1980s, most Mexicans who worked in the United States went back home after a few years. They're far less likely to do that — and far more likely to migrate in the first place — if Mexico becomes, once again, another semi-socialist basket case. Closing shut the "golden door" will make that scenario more likely.

E. Thomas McClanahan is a member of the Kansas City Star editorial board. Reach him at mcclanahan@kcstar.com.