Here's the skeleton of the argument with different flesh on it.
Feds: What are you doing?Ed
An Arizona cop: I just saw that guy run across the border from Mexico, so I stopped him. It is my accepted duty to protect and ser ...
Feds: But you can't do that. You see, there is already a law in place that protects the border, and your actions -- while roughly having the same effect as an enforced law regarding immigration -- contradict that law.
An Arizona cop: But you guys aren't enforcing the immigration law, so how can that be? How can a law that is not being enforced -- not being embodied into the actions of actual humans -- be contradicted?
Feds: What are you talking about?
An Arizona cop: Well, take the federal budget. It is something that, under normal circumstances, indirectly prescribes -- by outlining prospective cash flow -- a debt ceiling or debt limit, right?
Feds: Yeah, sure.
An Arizona cop: But what about when congress does not create a budget? What then?
Feds: Well, then you need a specific debt ceiling.
An Arizona cop: Why?
Feds: Because you need a debt limit, and if you cannot get one from a budget (because congress refuses to make one), then you need it as a stand-alone law in itself.
An Arizona cop: Why do you need some kind of a limit on debt?
Feds: Because of reality.
An Arizona cop: Please explain.
Feds: If you don't limit debt, then you get Germany in 1923.
An Arizona cop: Please elaborate.
Feds: Well, you inflate and borrow a little (you unilaterally expand credit) in order to boost economic activity or pay off cronies or whatever, but this triggered increase in activity can only be maintained by a continuous, geometric increase in inflation and borrowing -- until you reach the point where every able-bodied citizen would have to work around the clock in order to either physically print new money (to cover geometric increases in interest rates) or otherwise alter and adjust everything (e.g., the numerical denomination on money, the displayed prices in stores, etc.) upwards. An exponential increase in anything, eventually, will overwhelm any society that operates inside of physical reality.
An Arizona cop: Okay, I get it. Debt is not something than can ever be unlimited because, eventually, every human action taken will have to be in service to adjusting tools such as money, or signs in the window of stores that advertise prices, or whatever. I get it. It is not something that can ever be unlimited, because an unlimited amount -- just like an unlimited amount of heat, or an unlimited amount of radiation, or an unlimited amount of oxygen, etc. -- would, eventually, kill us all. Now let me bring this around to my point. Can we have unlimited immigration?
Feds: Alright, alright (you got me). I see where this is going. Don't mind me. Carry on with you doing your job then. Sorry to interfere!