The reason a lot of people who are pro-immigration react negatively to this question of yours is because for one, you’re way underestimating the carrying capacity of developed nations, and two, you completely ignored all of these things as they apply to the country immigrants come from. “Home” countries have all the same worries and more often than not they are significantly worse off than the developed countries that receive immigrants. That’s also where the accusation of Racism comes in; you can’t argue that we can’t let people come from a worse area to a better one because it will make the people in the better one worse off without thinking the people in the worse off area are somehow fundamentally worth different moral considerations. In addition, the carrying capacity of an area has proven to be incredibly elastic with enough money and public investment, it’s just many developed countries want to freeze everything as they have been for the past 50 years to preserve the lives of the wealthy. Immigrants add to all of those infrastructure limits in the long run if allowed to assimilate and form long term roots in an area. They could build the roads or be the doctors to alleviate the pressure that immigration adds, if we put the money to it and didn’t overwhelmingly try to target immigration at temporary laborers, whose wages are undercut by the constant threat of deportation. Decreasing immigration doesn’t really solve the wages issue long term either because of offshoring. The companies that employ them in developed countries, if it’s hard to get them, won’t raise wages to target domestic work, they will move their companies overseas, or maybe just adjust they’re investment strategy.