The charitable interpretation of immigration enforcement is that it ensures a nation does not get overwhelmed by people entering the nation -- in terms of its economy, bureaucracy, etc. I can see that argument that enforcing immigration maintains the economic inequality between individuals in the US and, for example, individuals in Guatemala, but controlled immigration ensures that a nation is capable of growing and supporting the immigrants that come in in the first place. After-all, immigrants are coming to a given country because of perceived advantages of that country, if too many immigrants come at a single time, those advantages may disappear.