You have to look at what uncontrolled migration actually did to some parts of the world. Take a look at some of the “mega” cities in Southeast Asia, where unfettered migration to the cities lead to something unlivable. There is also a massive lack of opportunity since everyone saturates the same professions (or simply just too many people). The city might already have the right amount Rickshaw drivers, but now it’s got 10x more because of mass migration from villages to cities. Now do that across the board for everything, software, retail, etc. I won’t even mention how housing and infrastructure are impacted. This kind of unfettered pipe opening will just lead to more unemployed, higher housing prices, and so on. You have to consider these things or else you get an unlivable disaster (India, Bangladesh - just take look at their mega cities as case studies, total disasters).
Oddly, a little bit of gate keeping would actually help. Everything in moderation, a little bit of open borders, a little bit of gate keeping, a little bit of everything - but not too much. Japan might be on the opposite side of things with a little too much gate keeping. We need vigilant balance (constantly reassess, and calculate the impact of a batch immigrants across say ... 30 years, and project how we need to adjust the pipeline to maintain a healthy growth/quality of life balance).
I’ll tell you what I can’t stand though. I can’t stand people that minimize the logistical element of increasing the population of a region to a moral and emotional argument. If you don’t carefully consider capacity, and reduce the argument to platitudes of ‘this has always been a land of immigrants’, you will certainly fuck us by adding to already growing issues of a hyper competitive economy where people are fighting tooth and nail for unstable low wage gig jobs, competitive and costly higher education, hyper competitive knowledge industries, and of course the hyper hyper hyper fucked and competitive housing market.
I want us to seriously consider why we want to add more to a pot where we are already getting cramped in a variety of ways.