&gt; We have no way of knowing what impact completely open borders would have on global GDP<p>The impact on developed countries from the enlargement of the EU is probably the best &quot;open borders&quot; experiment we can look at:<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;2004_enlargement_of_the_European_Union" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;2004_enlargement_of_the_Europe...</a><p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Enlargement_of_the_European_Union" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Enlargement_of_the_European_Un...</a>