The writer of an essay published by "The Economist" implicitly assumes that differences in culture and genetics do not produce differences in behavior among different ethnic or racial groups. Consequently, immigration does not negatively affect the pace of development for developing countries.
Yet, is that assumption true?
The Meiji Restoration (MR) in Japan proves that the assumption is false. MR began in 1868. During 25 years from that year, the Japanese aggressively modernized and became a wealthy, industrialized democracy. Japan became a Western power.
By contrast, the nations run by Africans or Hispanics are still poor and ignorant. This retarded development is not due to external oppression since most such nations are not controlled by an external power like Russia.
If all ethnic and racial groups have identical behaviors, then every nation would already be modernized (just like Japan) after 25 years of exposure to the West. That such an outcome does not exist proves that differences in culture and genetics produce differences in behavior among different ethnic or racial groups.
As for immigration, imagine the fate of Japan if, in 1868, somehow millions of Africans emigrate to Japan and become 30% of its population. Violence in its cities would increase dramatically. Under pressure from rioting Africans who despise the West, the Japanese government would be forced to abandon Westernization. The modernization of Japan would not have occurred, and it would remain an impoverished 3rd-world country. Today, 12 million Japanese would be living illegally in Russia and would be demanding that the Kremlin grant them a path to citizenship.
So, indeed, uncontrolled immigration into a developing country can severely retard its development -- if the immigrants are intellectually inferior to the native population.