Comment by wizzwizz4
1 day ago
"You can only stay in the country if you're sponsored by an employer" creates an environment where workers have low bargaining power, decreasing the pressure for good working conditions (e.g. high pay), which – among other things – has impacts on the working conditions for locals. One might say it "affects what the market will sustain" (personally, I don't think calling everything a "market" is insightful).
From a purely economic perspective, the ideal is no borders, and total freedom of movement – but, of course, there are reasons that people don't want that: the real world doesn't run on economics. Pretty much all of these measures are compromises of some description, with non-obvious (and sometimes delayed) consequences if you start messing about with them. Most arguments involving "$CountryName jobs for $Demonym!" ignore all that, and if that leads to policy decisions, bad things happen. (That's not to say there's no way to enact protectionist employment policies, but you'd need to tweak more than just the one dial if you wanted that to work.)
From an economic perspective the ideal is no borders if there are no significant differences between countries that would create an infinite surge in mobility. It's like electrical current, if there is zero resistance and a difference in potential, any short circuit will potentially destroy the entire circuit.
The "infinite surge in mobility" phenomenon only occurs if we model countries as infinite sources / sinks of people, and assume population movement has no impact on either country. Given both of these assumptions, the predicted phenomenon wouldn't cause any problems. Of course, neither assumption holds in real life; and if you re-do your models with more sensible assumptions, the phenomenon goes away.