This week saw the culmination of the great wall debate. President Trump made his case—one I generally agree with—and explained what an extra $5.7 billion (approximately 0.1% of the budget) would do for the security of our southern border. Democratic leaders Chuck Schumer and Nancy Pelosi immediately dismissed it. It is honestly surprising how quickly and thoroughly Democrats adopted the notion that a wall of any kind is such an obviously stupid and immoral idea. Well, is it? Let’s lay out the claims one by one:

• They’ll...