The 50,000 marchers who took to San Diego’s streets on April 9 to protest a House immigration bill that would make felons of undocumented immigrants in the United States and build a 700-mile border wall formed the biggest public demonstration this city has ever seen. Washington, D.C., was the site of an April 10 demonstration; with 870,000 marchers, it was the largest since the protests began last month.

The protests should send a message to politicians about the importance of immigrant workers to the national economy and character. The provisions in House Bill 4437 disastrously attempt to remedy a problem that can only be solved by acceptance of economic reality by social conservatives: In the global economy, labor, as well as capital, must be allowed to flow freely across borders.

Immigrants’ presence is a benefit, not a problem. Even if it was, building a wall wouldn’t fix it — job-hungry immigrants have circumvented every border security improvement so far.

Criminalizing illegal immigration is similarly absurd, given that recent estimates put the number of undocumented immigrants in the country at 12 million, a larger population than that of all U.S. prisons. Declaring them all criminals is likely to set off a major revolt.

We need an immigration policy that recognizes both the fluidity of the global economy and the contributions of immigrants. A guest worker program, where security and health-care concerns could be addressed before letting foreigners enter the country to work, sounds the most realistic.

The immigrant-labor flow across the border with Mexico will continue. The test of new legislation is whether it sensibly brings that exchange out of the dark, or continues to deny reality for a paranoid few.