Again, these are good points. As i like to say, there are two kinds of
political economy.
1) that supports the Economy (in general);and
2) that has been Politicised to supports a particular group of people
Nations are always looking out for themselves, but then so too are politicians (and their $supporters). =D
It is usefull, though, to seperate them. In that sense, the default logic of economics in a politicised argument should not (IMHO) be deferred to [just because]. It should be viewed as critically as a political policy (ie Art, not 'Science'...its not objective etc). And also debated thus and put into perspective also.
That's why many debates on immigration, etc get so far off track and/or are difficult to conclude with much progress. Folks conflating the two ideas and the standards of judgement, performance, opportunity cost, etc.
__________
On the substance of your point:
By not allowing companies to pay lower wages to foreign workers the wages of the local market is being protected.
The answer is yes, it is being protected. But this is a normal thing. Also what is being protected is the political Atom of . This is not something that should, in general, be commoditized. Thus, the "permeability" of the body politic (at the level of citizenry) is a legitimate debate, but its a political one, not a one-dimensional one in terms of wages/pricing etc.
So, to advance the debate, the question needs to be reframed a bit: what is the optimum level of social-permeability desired to grant title: citizen (or: greencarde, etc) for a nation state? And the you have to address issues of other kinds.
For example, do you care more about well to do foreigners than your less well-off existing compatriots? This is sort of an empathy argument (vs. efficiency). And in part its a longer term argument (are citizens more efficient working with some safety net underneath them?)/etc.
Right now in the usa, "merit" is not really a big goal of immigration policy. Can't say I agree with this, but the policy was revised to be more about human-right/family etc. So, if you are an immigrant general labororer US citizen it might be you get your cousin a greencard. But a regular no-strings PhD in astrophysics or whateve is not at any advantage vs the cousin of the general labourer (in fact just the opposite).
But family and the like is the ultimate sort of political argument. On the one hand, its very emotional (for those involved). And on the other hand, their are very specific special interests at play (important, process wise). So, you can see this is not something just totally possible to ignore, intellectually or practically.
Each country is different, though, in these ideas. Places like Australia have been know to offer more open merit-based immigration. Canada too, I believe.