Oh, I agree with that. I just believe Taney was wrong in this belief.
It referred to those who were full citizens -- those who could vote, run for any office, and who owned land (rich, white, adult male citizens). This excluded women, children, slaves, foreigners, and visitors.
One of the numerous problems with Taney's theory is that "the people" changed quite significantly between the 1780s and the 1850s, as the states expanded the franchise to include all white males. This was apparently just dandy with him.
So, states can legitimately, accordingly to Taney, change the definition of a "full citizen of the United States" in some ways but not in other ways. There is absolutely no justification for this distinction in the Constitution or in statute or common law. But Taney finds one, apparently because he is offended by the prospect of Africans as citizens and equals.
A much greater mind than mine has addressed the issue is considerable detail. Let me refer you to the man who led the successful fight against this iniquitous decision.
http://teachingamericanhistory.org/library/index.asp?documentprint=52
Wonderful speech, but Lincoln too was a man of his time. In that time, per the very words of his speech, while he was fiercely opposed to slavery, and equally a proponent of equal rights of citizenship for blacks, for all men whatever origin, yet he was a segregationist.
The Founders were not, and Lincoln's own retelling of our founding history regarding black and white people and its comparison to that of his own time, is telling. Fully integrated communities existed in America and in the Americas in the colonial era and onward. But as America the nation approached the times of Lincoln and Douglas, such communities in it became rarer. What is the reason for that dynamic? Compare us say to Cuba of the same era -- a similarly developed place in that era. Yet in Cuba racial intermingling was far more common. The social structure of Cuba of that era was similar to our south, racial intermingling was socially discouraged and there came to be laws against intermarriage. Yet the races still mixed. The social situation in Puerto Rico was less stratified, almost half the population was of racially mixed parentage. The major difference was slavery.
It was the growth of plantation slavery in America which drove racial segregation, even in those states that had abolished slavery. Even Lincoln, the great man and great intellect he was, could not avoid being poisoned by it.
Dred Scott was decided before the slavery amendments (13th, 14th and 15th) were passed. At the time of the decision, slaves were property.
Now, a state which abolished slavery could make freed slaves citizens of that state, but states had no power to make them citizens of the United States -- that power was reserved to the federal government.
Consequently, a free slave who traveled out of his state had no rights. The 14th amendment was passed, making the slave a "citizen of the United states" with limited rights (defined in later court cases) which were applicable in all the states.
"http://teachingamericanhistory.org/library/index.asp?documentprint=52"
Your link contains the words of Abrahan Lincoln discussing the sacredness of the U.S. Constitution which he believed protected the rights of negros. This, coming from a man who a) suspended habeas corpus, b) did not believe in the constitutional right of the states to secede from the Union, and c) was against mixed-marriage (that's too much equality, I guess).