That's because you forgot several other "postulates" that form part of that legal argument. Among them (this is not an exclusive list) are the Commerce Clause of the Constitution, and various canons of legal construction, including the one that holds that while a newer enactment generally has precedence over an older one, to the extent possible a newer enactment should also be read so as not to minimize conflict with an older one unless it explicitly seeks to reverse the effect of the older one.