Veronique: Your call for humility in government decision-making, for not being fooled by the “pretense of knowledge,” is one that should always be before us. While the left is most desperately in need of this insight, policymakers on the right need constant reminder as well, as you suggest with regard to the Iraq war.

While this is especially necessary to keep in mind in matters of war — no plan, after all, survives contact with the enemy — it is curious that many on the right never allow the caution of gradualism and prudence to interfere with their calls for radical immigration schemes. Marco Rubio’s (never renounced) support for doubling immigration from 1 million a year to 2 million, Ted Cruz’s call for quintupling of H-1b visas, libertarian economists’ and the Wall Street Journal’s perennial cries for elimination of any limits on immigration — none of these is informed by the words you would have liked to have heard from Jeb regarding the Iraq misadventure: “we must be more humble about the possibility we’ll be very wrong about the consequences of our actions.”

Our current immigration policies are already pretty radical, and require moderation, but even that moderation could be done gradually. For instance, abolishing the Visa Lottery and the category for adult siblings of U.S. citizens would result in only about a 10 percent reduction in future legal immigration — then we can look for unintended consequences that might cause us to rethink the policy. I’d prefer simply to abolish H-1b visas, but why not first try a more modest change and see how it works: clear away the bureaucratic underbrush and simply charge employers $100,000 for each visa, which they’ll gladly pay if they need the person as much as they say they do. Even regarding amnesty, rather than legislating grandiose schemes like Rubio and Schumer’s Gang of Eight bill, why not first try increasing the cap on the already-existing “cancellation of removal” process from 4,000 a year to 50,000, and let judges examine individual cases and grant green cards only to the most sympathetic cases — those whose deportation would cause (as the law requires) “exceptional and extremely unusual hardship” to U.S. citizen or permanent-resident spouse, children, or parents.

Hayek noted that “If man is not to do more harm than good in his efforts to improve the social order, he will have to learn that in this, as in all other fields where essential complexity of an organized kind prevails, he cannot acquire the full knowledge which would make mastery of the events possible.” Immigration enthusiasts would do well to heed his words.