<MCRed> is arguing (admittedly in a rant-y kind of way) that the U.S. Constitution is a document that grants limited and specific powers to the federal government and reserves the rest for the states and the people. That argument says those powers do not include the ability to regulate money exchange. An implication of that argument is that nearly all law enforcement would be left to the states -- so your hypothetical sex slave ring would be prosecuted by the states, and in fact every state currently has a law on its books making such a conspiracy illegal. And in fact most criminal prosecutions are already done by state governments.
Again, I'm not saying what I would prefer as a normative matter, just that it looks like you're talking past each other to some extent.