Are you claiming that slavery is constitutional?
How does that square with the 4th amendment against unreasonable search and seizure? The fugitive slave laws allowed anyone to seize anyone they thought might be a slave. Clearly unconstitutional. Also clearly kidnapping! I'd like to hear how you would not consider this kidnapping.
How does it square with the 5th amendment? No one can "be deprived of life, liberty, or property, without due process of law." Kidnapping someone clearly violates this amendment.
The 6th and 7th amendments guarantee the right to an impartial jury and a jury trial - however the laws the south wanted to force on the north (a hypocritical violation of states' rights) allowed people to be kidnapped without going through these processes.
You can argue that the constitution is contradictory, but you cannot reasonably argue that the fugitive slave acts do not violate the bill of rights.
> I don't think you have fully thought through your position.
You are ignoring the facts. The south's stated reason for leaving the union was to continue the institution of slavery. The modern "states' rights" argument _regarding the war_ is an attempt to ignore that the state right explicitly called for by those states was the right to own other people.
It was until the Thirteenth Amendment was passed, yes.
I think you have some serious learning to do about the Constitution.
As for how the Bill of Rights was interpreted to be consistent with the fugitive slave provision of the Constitution, that's simple: the jurisprudence of the time did not apply the Bill of Rights to slaves. I'm sure this will seem very shocking to you, but it's quite clear from the historical documents (see, for example, my reference to the Dred Scott decision upthread).
> you cannot reasonably argue that the fugitive slave acts do not violate the bill of rights
Perhaps you can't, but the judges and juries of the time had no problem doing so at all. See above. Even abolitionists did not make this claim. They claimed that slavery was wrong and that laws such as the fugitive slave law were unjust, but they never claimed they were unconstitutional. Their response to provisions like that in the Constitution was to say that the Constitution itself was unjust; for example, William Lloyd Garrison called it "a covenant with death and an agreement with hell". And they were perfectly ok with violating the Constitution in the name of what they believed to be the greater good of abolishing slavery. But they never argued that the Constitution's fugitive slave provision was inconsistent with the Bill of Rights, because nobody believed that to be the case.
> You are ignoring the facts.
No, I'm not. I just appear to have a much better understanding of their historical context than you do.
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.)
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.
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. But just claiming that the Constitution doesn't allow fugitive slaves to be returned to their owners, and calling doing so "kidnapping" without any supporting argument, when the Constitution has an explicit provision that requires fugitive slaves to be returned to their owners, is nonsense. You can't just ignore parts of the Constitution you don't like.
> only the south was wrong here
I don't think you have fully thought through your position.