When the discussion is about economics (the topic I have studied at uni) most comments are just plain wrong and show a complete ignorance about the topic.
If one wants a counter argument to "too many people for the economy" one can start here : https://www.jstor.org/stable/2523702?seq=1
"Using data from the Current Population Survey, this paper describes the effect of the Mariel Boatlift of 1980 on the Miami labor market. The Mariel immigrants increased the Miami labor force by 7%, and the percentage increase in labor supply to less-skilled occupations and industries was even greater because most of the immigrants were relatively unskilled. Nevertheless, the Mariel influx appears to have had virtually no effect on the wages or unemployment rates of less-skilled workers, even among Cubans who had immigrated earlier. The author suggests that the ability of Miami's labor market to rapidly absorb the Mariel immigrants was largely owing to its adjustment to other large waves of immigrants in the two decades before the Mariel Boatlift."
There are many causes explaining unemployment some due to macroeconomic factors such as the monetary policy, others due to regulations of the labor market, others due to the lack of innovation, ..... They have been studied in depth. But "too many people for the economy" is not one of them.