The Federal Government Has No Immigration Powers

Radar, the Constitution is but an instrument of "We the People" and regardless as to whether or not the Constitution grants the federal government authority to regulate immigration, we the people have.

The Constitution is not like documents purported to be derived from a higher power (e.g. the Bible representing the word of God), it is acknowledged to be a product of people and people are known to be fallible and to have their limitations. The Constitution will continually be subjected to trial by fire in order to determine its current relevancy in part; or, as a whole. To promote its survivability, it was created as a living document which is why a fundamental reading will never supplant interpretation for the times. That which is now unconstitutional may become constitutional in the future and vice versa. It is essentially the burden of pundits against change to demonstrate that "We the People" are better served by strictly adhering to the Constitution in its present form; because, if push comes to shove, we the people can modify or rescind it.

You'll have to come up with a better rationale for why the federal government shouldn't regulate immigration other than because the Constitution doesn't provide for it. The Constitution works for the people, not the other way around.