This turned out to be quite an angry post, so a quick preface: All of this is a knee-jerk response to a single sentence in your post. So, you know, please take with a grain of salt, not personally, etc..

I have to admit, it's a little bit depressing to see someone just use a straight-out lump of labor argument against immigration.

I can deal with people who believe immigrants tend to be criminal and who are concerned for their family's safety - they're wrong, but they're afraid, and fear's got a way of overriding statistical reason. I can deal with people who believe immigrants will bring poor institutions from their countries of origin - I think their evidence is weak, but I realize there's a lot at stake in keeping the global North rich and well-run, so I can see at least some reason for caution. I can even deal with the racists by letting my eyes glaze over for a while. People who think that brain drain hurts the country of origin too much... believe in a greater amount of responsibility that individuals have for their nations of birth than I do, but okay, at least they're coming from what they believe is a position of compassion. And so forth - I can sympathize with, understand, or at least ignore most arguments against more open immigration, even if I disagree with them.

But just "stop importing poor foreigners who undercut American wages"? What do you think makes your work valuable in the first place? I mean, I assume that like with most people in a modern economy, very little of what you consume comes from what you yourself produced. Your work is valuable because other people have demand for its results, and will exchange some of their own surplus for it. The more surplus there is to go around, the more there is for you to get. You might have to specialize more to compete in a bigger market, but you're surely capable of it. Even the poor generally are. If nothing else, in case of immigration to the USA, the natives tend to have the distinct advantage of being literate and generally conversable in English.

So please at least have the rational selfishness to ask for more surplus! Yes, the one guy who moves in to your tiny geographic area and works in the minuscule sliver of what you produce in the economy will make your life more complicated, because now you'll have to compete with them. But for that guy, there'll be thousands of others whose greater productivity you will now get to enjoy. Maybe if you were the Immigration Czar, you could be very selfish and decide that that person doesn't get to move in but everyone else does. But if you want to make a policy that lets all selfish people benefit, then you have to let everyone face more competition and get more surplus.

To in fact not undercut my own point: I'm not claiming that that's the whole story. You might believe that maybe there will in fact be less surplus overall in the long run if you open up immigration, or you might believe that the fruits of greater productivity will go to people who don't deserve them. Again, those are concerns that I can in fact see reason in. Not that many people actually believe that they live in a world where the only difference between labor in a rich country and labor in a poor country is that the former are more productive because of where they live. In more advanced territory, I might even have to deploy moral arguments, like how unconscionable it is to not let people - individuals of just as much moral worth and agency as you or I, or indeed us behind the veil of ignorance - work in your country because they were born on the wrong side of a border. But I won't do it for lump-of-labor. It doesn't show enough understanding of economics to be worth a moral argument.