There is a law against kidnapping in Texas as well. It isn't necessary that there be a federal law.
None of this really deals with the fact that Congress isn't given the power to define crimes other than the three listed in the constitution. (Excepting Washington DC of course).
I think this all comes down to a disagreement in interpretation of Amendment X. And when there is disagreement, whose argument will prevail? Does your interpretation carry more weight than mine? Do you matter more than me? Do I matter more than you? So how are these interpretive disputes solved?-----why, the answer to that is given in the Constitution, too. Ta-daaaaah! The Judiciary Branch! The supreme Court, with the exceptions listed in Article III, section 2, shall have "appellate jurisdiction, both as to Law and Fact, wich such exceptions, and under such Regulations as the Congress shall make."
In other words, it's useless for you and I to be arguing back and forth over Congressional authority, because such questions have already been asked and answered, in the Constitution, under all three branches of government and the state governments, with the Supreme Court having appellate jurisdiction.
I'm rather glad you and I could disagree without tearing each other up. This is my last word on the subject. As you well know, unwritten law says women always get the last word, but if you would like to have it, whether you're male or female, you have my leave. :-)