Another example of the "Living Document" theory.
In this case, Congress did not envision a future congress who was intelligent enough to discern that we needed a labor source, but had an eviscerated nutsack and was therefore incapable of standing up to the labor unions. They further did not anticipate the willingness of the entire union to tolerate a permanent class of disenfranchised constitutional non-entities as long as they would cut their grass, build their houses, and wash their cars. Finally, they sure as hell did not anticipate that those who profess loudest to be constitutional literalists would advocate the mass deportation of persons whose "crime" was to sneak across the border, rather than figure out a way to admit them to citizenship. You see, they had just fought a nation destroying WAR over the rights of people vs the rights of states, and did not anticipate those who profess the loudest that they wanted to uphold the traditions of freedom being the same persons who essentially don't give a sh!t what we do with illegal immigrants, so long as their wage standards aren't affected, and they can protect their place at the slopping trough for federal handouts.