See also: precautionary principle, swamped, gradual versus sudden open borders, and moral versus practical arguments

Among those who are generally supportive of expanded immigration, there are some who support moderately more open borders. Such supporters typically do not buy the libertarian case for open borders in its entirety, but may be convinced by some of the utilitarian and egalitarian arguments. They may also, based on the precautionary principle, be skeptical of radical changes to immigration policy. These people generally start from the status quo and then consider what changes can or should be made.

On the other hand, there are people who support radical open borders. These people generally argue strongly from the presumption of open borders, and then ask questions about when, if ever, immigration may be limited.

The moderate versus radical distinction has a slight variant: those who support radical open borders, but wish this to be achieved through gradual increases in immigration quotas.

Blog posts and articles

• Why open borders won’t work and Inconvenient questions about immigration by Tyler Cowen, where he argues that even though he is supportive of substantial increases in skilled and unskilled immigration, he does not favor open borders because it would undermine democracy and living standards of everybody, including the immigrants. Cowen further clarifies his position in The Open Borders attack.

Responses by open borders advocates

In his piece Why Should We Restrict Immigration? (PDF, 20 pages, ungated), part of Cato Journal Winter 2012, Bryan Caplan argues that instead of embracing moderate open borders out of fear of radical open borders, it makes sense to work gradually towards radical open borders and stop at any stage if things seem to start getting worse:

If you embrace something like the Precautionary Principle (Sunstein 2005), this is a powerful objection to immediate open borders. The society we have works extremely well by world and historic standards. If you live in the First World, you’re doing fine. Why take chances?

From an amoral, risk-averse point of view, there is no good response to this objection. But if you take the moral presumption in favor of free migration seriously, this is a weak argument indeed. Immigration restrictions are not a minor inconvenience we impose on the rest of the world for our peace of mind. Immigration restrictions literally ruin many millions of lives—forcibly denying people the opportunity to do business with their best customers. “We’re trapping millions in Third World misery because we know that free migration has very bad consequences” arguably overcomes the presumption in favor of open borders. “We’re trapping millions in Third World misery because there’s a small chance that free migration has very bad consequences” does not. Think of the moral progress that the Precautionary Principle would have precluded: until a society tried freedom of religion or the abolition of slavery, no one could be sure the experiment wouldn’t end in disaster.

In any case, the Precautionary Principle lends no support to the status quo. Existing research confirms that moderate liberalization of immigration has excellent overall consequences. If the “out of sample” problem bothers you, the obvious solution is to expand the sample gradually. Step one: liberalize slightly more than any other country. Step two: see what happens. Step three: in the absence of very bad consequences, liberalize a little more and return to step two.

See also:

• If Open Borders Are Instituted Gradually, What Should Be The Initial Number of Immigrants Admitted? by Joel Newman, August 9, 2013, for Open Borders: The Case.
• Slippery slopes to open borders by Vipul Naik, February 11, 2014, for Open Borders: The Case.