On Sunday thousands of people are participating in a March for America on behalf of immigration reform. And plenty will be debating: Should we support or oppose immigration? The evidence suggests that immigration benefits Americans by expanding output and lowering prices. And I cannot think of a valid principled objection to immigrationwhether legal or illegal. However, plenty of people certainly disagree. One point of contention that appears throughout the immigration debate concerns the role of restricting immigration in ensuring cultural integrity.