Interesting information from brilliant constitutional law scholar Thomas B. McAffee, The Constitution as Based on the Consent of the Governed–Or, Should we Have an Unwritten Constitution?, n.110:

Interestingly, although modern scholars have ridiculed what they took as a “federalism” reading of the Ninth Amendment, given that the text itself refers to “rights,” in August of 1789, while the nation considered whether it ought to adopt the Bill of Rights, William L. Smith endorsed the Ninth and Tenth Amendments on the grounds that “they will go a great way in preventing Congress from interfering with our negroes after 20 years or prohibiting the importation of them.” Letter from William L. Smith to Edward Rutledge (Aug. 10, 1789), reprinted in Creating the Bill of Rights: The Documentary Records from the First Federal Congress 273, 273 (Helen E. Veit et al. eds., 1991).

This comment illustrates a couple of interesting things. First, that the Ninth Amendment had a federalist (federal-power-limiting) function, rather than the individual-rights function ascribed to it today. And, second, it’s ironic that the Ninth is proclaimed by the politically-correct libertarian centralists, when it was here cheered by a slavery advocate… Interesting…
See also Akhil Reed Amar, The Bill of Rights: Creation and Reconstruction, at 123-24:

As Professor McAffee has shown, the [Ninth] amendment’s legislative history strongly supports an enumerated-powers, federalism-based reading. The obvious counter-argument–chanted like a mantra by most mainstream scholars–is that this reading renders the Ninth Amendment wholly redundant of the Tenth [and thus they favor an individual-rights reading of the Ninth instead — NSK]. To be sure, on a federalism-based reading, the Ninth and Tenth fit togther snugly, as their words and their legislative history make clear; but each amendment complements the other without duplicating it. The Tenth says that Congress must point to some explicit or implicit enumerated power before it can act; and the Ninth addresses the closely related but distinct question of whether such express or implied enumerated power in fact exists. In particular, the Ninth warns readers not to infer from the mere enumeration of a right in the Bill of Rights that implicit federal power in fact exists in a given domain. Thus, for example, we must not infer from our First Amendment that Congress was ever given legislative power in the first place to regulate religion in the states, or to censor speech. … [T]he federalism roots of the Ninth Amendment, and its links to the unique enumerated-power strategy of Article I, help explain why no previous state constitution featured language precisely like the Ninth’s–a fact conveniently ignored by most mainstream accounts. … by the 1860s the federalism reading of the Ninth Amendment had faced considerably, as many post-1791 state constitutions did echo the wording of the Ninth Amendment, but not the Tenth. And so clauses that originally dovetailed later came unglued; thus we now tell ourselves that the Tenth Amendment is about states’ rights while the Ninth is about individual rights.

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