I would redirect our friend (along with Taney) to the ‘s dissent:
@John McLean
In the argument, it was said that a colored citizen would not be an agreeable member of society. This is more a matter of taste than of law. Several of the States have admitted persons of color to the right of suffrage, and in this view have recognised them as citizens; and this has been done in the slave as well as the free States. On the question of citizenship, it must be admitted that we have not been very fastidious. Under the late treaty with Mexico, we have made citizens of all grades, combinations, and colors. The same was done in the admission of Louisiana and Florida. No one ever doubted, and no court ever held, that the people of these Territories did not become citizens under the treaty. They have exercised all the rights of citizens, without being naturalized under the acts of Congress.
The rest of the opinion is available here.
This decision was the worst even given by the SCOTUS: even in the 1850s legal norms, which allowed slavery, this decision was mediocre and mainly politically-driven in an attempt to legislate from the bench.to protect and enshrine slavery forever.
@checkmate
Here.
This guy triggered the Civil War: Northern politicians soon feared the slave-owners would take over most of the territories and even argue they could bring their slaves in the free states, and went to vote for the GOP.