Slaughterhouse and the P & I Clause of the 14th Amenment

"No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States."

The Court interprets this clause very narrowly in some respects--see p. 450-452--protection when on the high seas, writ of heaeas corpus, right to use navigable waters of the United States.  

But importantly, the right of a citizen of the United States "of his own volition" to "become a citizen of any State of the Union by a bona fide residence therein, with the same rights as other citizens of that State."

This, of course, was aimed directly at the Dred Scott decision--all persons, including the former slaves, if born in America, are not only citizens of the United States, but they also have the right to become an equal citizen of any state of their choosing. Citizens choose states, states don't choose citizens.

This is an extremely important privilege of United States citizens that no state may abridge.