The very idea that unions would endorse legalizing illegal immigrants, as the country’s two big labor federations did this month, strikes some as absurd. Americans have a hard enough time competing with cheap foreign labor. Why undercut them within our own borders? Especially with millions of citizens losing their jobs?

These questions deserve an answer since the bad economy will only strengthen the stiff winds of opposition that President Obama will have to fight if he is going to win the sweeping immigration overhaul he has promised. Legalization was already politically treacherous thanks to the tireless work of restrictionists who have spent years denouncing illegal immigrants as harmful to the country’s health. They have long compared the undocumented to invaders and parasites; it’s a very short distance from there to scabs.

To understand why that view is misguided, it helps to remember that the country has largely bought that argument and spent decades and billions to seal the border as tightly as possible.

It stages raids to pull people off assembly lines and out of their beds and cars. It has added hundreds of thousands of prison beds to hold illegal immigrants and enlisted local police officers to enforce federal laws. It has done everything it can to make illegal immigrants miserable in the hope that they will abandon their jobs, houses and citizen-children and tell everyone back home to forget about America. And how has that worked? It hasn’t.