You described several situations without quantifying anything. Also, you're not really making an argument for immigration...you're more accurately making an argument for "more people (regardless of origin)" are better for the economy. I do not believe this is the case overall. There are very few industries where jobs cannot be filled due to lack of applicants or lack of skills that can only be found outside our borders.. Conversely, there are plenty of examples in the US and worldwide where population density (more people) does not equate to economic prosperity. In fact the opposite is true in many cases. If immigration was an automatic economic boost, then why aren't the leaders of countries worldwide doing everything they can to lure immigrants to relocate into their country??!!??!