According to ethnic nationalists like Salter, market liberalism is maladaptive for two reasons. People in liberal societies tend to have low fertility rates, and liberal societies tend to have open borders that allow the immigration of outside groups with high fertility rates. If this continues into the future, eventually the native ethnic groups in liberal societies will become small minority groups, or they will go completely extinct.
Salter has elaborated his reasoning in his book On Genetic Interests (2003), which has become one of the most influential books among ethnic nationalists today, particularly the “alt-right” white supremacists in the United States. In his review of Salter’s book, American white supremacist Jared Taylor claimed that Salter provides “a scientific justification for racial consciousness and activism.”
Frank K. Salter, "Estimating Ethnic Genetic Interests: Is It Adaptive to Resist Replacement Migration," Population and Environment 24 (2002): 111-40.
Frank K. Salter, On Genetic Interests: Family, Ethny, and Humanity in an Age of Mass Migration (New York: Peter Lang, 2003).