The difference being that slaves had no legal status as citizens of any State, and there was no such thing as citizenship of the common government (United States) at that time, which is why Dred was first dismissed for having no standing in the court.
This notion that there was no such thing as US citizenship, only state citizenship is another falsehood I've seen repeated on these threads. The fact is that the Constitution refers to US citizenship several times, and the Naturalization Act of 1790 specifies the process:
Be it enacted by the Senate and House of Representatives of the United States of America, in Congress assembled, That any Alien being a free white person, who shall have resided within the limits and under the jurisdiction of the United States for the term of two years, may be admitted to become a citizen thereof on application to any common law Court of record in any one of the States wherein he shall have resided for the term of one year at least, and making proof to the satisfaction of such Court that he is a person of good character, and taking the oath or affirmation prescribed by law to support the Constitution of the United States, which Oath or Affirmation such Court shall administer, and the Clerk of such Court shall record such Application, and the proceedings thereon; and thereupon such person shall be considered as a Citizen of the United States.The clause protected against the practice of slaves being freed (or stolen depending if youre talking ideology or law) once they crossed State lines into non-slave states or Federal territories - such acts were never done Constitutionally - moral relativism is not the law.
No. That would be Article IV, Sections 1 and 2.