We have no way of knowing what impact completely open borders would have on global GDP, so to throw around predictions like doubling global GDP is just ridiculous. Economies are complex systems and moving around tens to hundreds of millions of people is such a massive change that you can&#x27;t possibly accurately model what would happen. I doubt the economies of developed countries would react positively to an influx of tens of millions of people.<p>But the people advocating this usually aren&#x27;t advocating for truly open borders, they are usually advocating for more IT workers, so they can reduce the costs to their companies.<p>Let&#x27;s imagine for a moment what would happen if we allowed just the small subset of unlimited immigration that people are really pushing for--an unlimited number of immigrants who have CS degrees. What do you think would happen to programmer salaries when 10 million new programmers arrive next year?