The right to own them was in the Constitution as was the more generalized right of property.
No one was proposing a ban on ownership of slaves, but the Federal Government did have the right, established under the Northwest Ordinance, to restrict ownership of slaves within Federally supervised territory.
Unless you accept my "conjecture" that expansion to new markets to keep the slavery Ponzi scheme floating was the driving force behind secession, why was it that South Carolina should care so much about what happened in territories a 1000 miles away?
James Madison had strong views on whether the Congress had any constitutional authority to pass laws concerning the new territories:
Congress has undertaken to do more: they have proceeded to form new states, to erect temporary governments, to appoint officers for them, and to proscribe the conditions on which new states shall be admitted to the confederacy. All this has been done; without the least color of constitutional authority
(Federalist #38)
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The Missouri Compromise of 1820 was ruled unconstitutional in Dred Scott. Chief Justice Taney said Congress did not have the authority to restrict slavery in any territories. Slaves were property, and the restriction of property without due process violated the Fifth Amendment of the Constitution.
In Strader v. Graham (1851), for example, the Supreme Court ruled that the Ordinance was no longer in force in the states formed in the northwest territory.
Many of your arguments are a rehash of material already covered by NS. Please see post #65.
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why was it that South Carolina should care so much about what happened in territories a 1000 miles away?
Because the government used the excuse of the 'Compromise' to prevent States from deciding whether or not they would be slave-holding States. If all the territories that became States were allowed to maintain the slave holding status they had had all along, there would have been more slave holding than non-slaveholding States.
The federal government was "Stacking the deck?" in an effort to restrict something they legally had no say in.