> If you want to argue that the explicit Constitutional provision about fugitive slaves (Article IV, Section 2, last clause) is inconsistent with other provisions of the Constitution, you can try to make that argument
The fugitive slave provisions of the Constitution were, by definition, consistent with the Constitution, however morally repugnant they were. The Fugitive Slave Act of 1850, OTOH, provided for the summary detention of accused escaped slaves by affidavit without warrant or probable cause or even any establishment of a reasonable basis, denied accused escaped slave the right to be heard in their own defense, denied them jury trial on the accusation, denied them trial before a judicial officer on the accusation, allowing the accusation to be heard by special commissioners who were paid a premium for ruling that the accused was, in fact, a fugitive without even a pretense of evenhanded justice, and commandeered state officers to assist with enforcement. On any reasonable reading—notwithstanding that its purpose was Constitutionally valid—it violated the 4th, 5th, 6th, 7th, and 10th Amendments, and the suspension clause.
(The Fugitive Slave Act of 1793 has a subset of the same problems.)
> On any reasonable reading—notwithstanding that its purpose was Constitutionally valid—it violated the 4th, 5th, 6th, 7th, and 10th Amendments, and the suspension clause.
The Supreme Court in the Dred Scott decision did not take this position. They took the position that the Constitution's protections simply did not apply to slaves. (In fact the decision said that those provisions didn't even apply to free blacks.)
Of course you can say that the Supreme Court was simply wrong. But under our system of law, the Supreme Court's rulings on Constitutional provisions are final unless overridden by an amendment--as the Dred Scott decision was overridden by the Thirteenth Amendment. So as a matter of law, the fugitive slave laws were Constitutional until the Thirteenth Amendment was passed. Just as, for example, it's Constitutional (unless a future Amendment changes things) for Congress to regulate a farmer's growing of wheat for personal use under the Commerce Clause (Wickard v. Filburn), or for a city to seize people's homes and turn them over to a private developer under the eminent domain power (Kelo v. New London). You might think those decisions were wrong (I do), but they're still the law of the land unless and until a Constitutional Amendment overrides them.
The fugitive slave provisions of the Constitution were, by definition, consistent with the Constitution, however morally repugnant they were. The Fugitive Slave Act of 1850, OTOH, provided for the summary detention of accused escaped slaves by affidavit without warrant or probable cause or even any establishment of a reasonable basis, denied accused escaped slave the right to be heard in their own defense, denied them jury trial on the accusation, denied them trial before a judicial officer on the accusation, allowing the accusation to be heard by special commissioners who were paid a premium for ruling that the accused was, in fact, a fugitive without even a pretense of evenhanded justice, and commandeered state officers to assist with enforcement. On any reasonable reading—notwithstanding that its purpose was Constitutionally valid—it violated the 4th, 5th, 6th, 7th, and 10th Amendments, and the suspension clause.
(The Fugitive Slave Act of 1793 has a subset of the same problems.)