Selfish Reasons to Have More Kids is a 2011 book arguing that people often work too hard in child-rearing, and as a result, they are scared off the idea of having kids. Caplan's book urged parents to relax with respect to child-rearing. He also argued that as the perceived costs (in terms of child-rearing expense and effort) of having kids fell, it made sense to have more kids based on the basic theory of supply and demand. The book was reviewed in Wall Street Journal. The book was also reviewed by The Guardian, RealClearMarkets and the Washington Times.
Caplan has identified himself as a pacifist on pragmatic grounds and has summarized his "common-sense case for pacifism" using three steps:
The immediate costs of war are clearly awful
The long-run benefits of war are highly uncertain
For a war to be morally justified, its long-run benefits have to be substantially larger than its short-run costs
In July 2011, Caplan debated his case for pacifism with Ilya Somin.Sheldon Richman claimed to find Caplan's arguments more convincing in the debate. In a February 2013 LearnLiberty-sponsored debate with Jan Ting at the Students for Liberty conference, Caplan used a slightly different breakdown of the case for pacifism, using four steps instead of three.
Caplan is a vocal proponent of open borders, submitting that immigration restrictions keep the poor locked in a prison of poverty, limiting both freedom and prosperity. He has made his case in an article for the Cato Journal and numerous other writings on his blog and elsewhere, as well as in talks and debates. A talk titled Immigration restrictions: a solution in search of a problem by Caplan in September 2010 to the GMU Economics Society, sponsored by the Future of Freedom Foundation, was praised by David R. Henderson and Jacob Hornberger.
Caplan was cited as one of the leading proponents of the open borders position in an article in The Atlantic by Shaun Raviv. He has also been quoted in other mainstream press pieces on immigration in outlets such as the Huffington Post and Time Magazine.
In September 2012, Caplan participated in a Cato Unbound debate along with Steven Horwitz, George Selgin, and Antony Davies on the value of Austrian economics. In his response essay, Caplan reiterated some of his earlier critiques of Austrian economics and also argued that Austrians' rejection and/or neglect of behavioral economics was puzzling given their philosophy of subjectivism.
The bulk of Caplan's academic work is in public economics, especially public choice theory. He has agreed with political economist Donald Wittman that traditional public choice has reached conclusions inconsistent with the canonical assumption of voter rationality; many of his publications examine the effects of relaxing this assumption, an idea Caplan dubbed rational irrationality. In a series of exchanges with Wittman, Caplan defended many of the conclusions of public choice while agreeing that Wittman's criticisms hold under the assumption of voter rationality. Caplan has also done empirical work on public opinion which suggests voters indeed hold systematically biased views about economics.
Caplan has written about the problem of preference falsification in the face of social pressure and said that: "I think the wisest course is to turn the other cheek. I will not call anyone else names, express my disappointment in them, or try to shame them."
Caplan has called himself a "betting man" and stated that people who make predictions about the future should be willing to make bets about their claims. He has proposed and made a number of bets with others. He has been critical of the view offered by Tyler Cowen and Noah Smith that financial portfolios are a better test of one's true beliefs than bets.
In a Cato Unbound piece, Caplan identified himself as a natalist – he believes that more people are good for the world. He identifies himself as a fan of Julian Simon, who was a proponent of the idea that larger populations lead to greater technological progress and a higher standard of living for all.