I'd focus a lot more on the low-skill jobs than the higher-skill ones, when it comes to immigration. I see it as preferable from all three key perspectives:
(1) The perspective of the immigrants. Low-skill immigrants have the fewest options in their home countries and are likely to suffer the most if they can't come here (whereas higher-skill immigrants will be able to find decent jobs even if they can't emigrate). Thus, taking on low-skill workers will mean greater per-worker diminution in suffering than taking on higher-skill workers.
(2) The perspective of those left behind. If we skim off the highest-skill workers from developing nations (often after their countries have invested lots of money educating them to be a hope for the future), we're screwing over those countries -- making it harder for them to develop into more productive and prosperous nations. By comparison, if we siphon off workers who would often be a burden to their home countries, but are able to provide valuable low-end services in a wealthier nation, we are easing the path for those nations to become prosperous (they get revenues from money the workers send home, without those people burdening infrastructure and services there).
(3) From the perspective of native-born Americans. If we bring in high-skill workers, we are undercutting the bargaining power of people who are already here and competing for those jobs. For example, if you've just invested $100k in education to be able to fill a job as an engineer, only to find you can't earn enough to pay off your loans because the employers have imported cheaper alternatives (who lacked those high educational costs), you're going to be in rough shape. By comparison, if we bring in lower-skill workers from abroad, a lot of the work they'll do will just be for stuff that would represent an uncompensated burden for Americans if the immigrants weren't here making those things more affordable. For example, if it's cheaper to get your lawn mowed by an immigrant, you're less likely to just suck it up and do it yourself. So, it makes your life better even as it makes the immigrant's life better, and nobody is worse off. It would also displace some work that would otherwise be automated (e.g., more immigrants flipping burgers in the US, rather than more Chinese people in China building burger-flipping machines for export to the US). And it could provide upward pressure on native-born Americans' careers, making advancement easier (for example, would you rather be the housekeeper who is on her knees scrubbing a toilet, or the person who manages a team of immigrant housekeepers, while leveraging your superior English language skills and cultural knowledge to be the interface with the customer?)
I'm open to the idea of specific short-term STEM imports to address acute spot shortages. But we should not lean on that as a fix to a chronic shortfall of skills in those positions. Rather, we should invest in training up the native population to take those jobs, while the jobs they vacate as they move to those higher-skilled positions get filled by lower-skill immigrants.
Yes, but that doesn't change the fact the dependency ratio is growing rapidly and soon will get into Japanese territory. Prior to the Boomers, we had a situation where every generation was at least a little bigger than the prior one, which set us up for some easy math when it came to things like funding retirements. Retirees would have a larger generation right behind them, and then an even larger generation in the junior positions following that one. But the Boomers were followed by a much smaller generation, and so even now that there's a trivially larger generation coming along, the math just doesn't work out. You need a LOT more workers than retirees for things to go smoothly (e.g. 5 working-age people for every retiree), and we're moving quickly to a situation where workers will only outnumber retirees by a fairly small margin (e.g., a bit more than 2 working-age for every retiree), making things very difficult. We can fix that with immigration.
