It's curious to me that you skipped over the line "no other reading of the document makes sense."

What do you think Art. I, Sect. 8 is referring to? Were we going to naturalize the residents of Europe and make them U.S. citizens? My time is brief this morning, and I don't have time to go look at the Constitution, but it also sets rules for the federal government's role when the states wish to "import" large numbers of people -- so there is a secondary authority to regulate immigration if the primary one I cited is unsuitable. In any case, you can't weasel around the fact that the Constitution sets authority for the United States to regulate trade and immigration across its own borders. It does, and it always has.