Referring to the "Southern slave holding states" is a correct manner of describing who they were talking about, but that does not equate to mean "We are leaving because of slavery." They are leaving because of Tyrannical actions by the Federal government in raising an army to oppress them.
I know you very very badly want to make everything related to the civil war about "slavery", but Virginia has not made a statement to the effect that they are leaving because the Union government is threatening slavery. It has made a statement to the effect that they are leaving because the Union government is threatening states who left. Presumably Virginia would have been just as incensed had the US Government attacked Massachusetts and Connecticut if they attempted to leave, just as they talked about doing at the Hartford convention in 1812.
You may not be aware of this, but *ALL* the Southern states were slave holding, but the Federal government had no problem with that. They offered the "Corwin Amendment" to guarantee the right of states to have slaves.
Yes, I’m aware of that proposed Corwin Amendment and the other political matters on the forefront of 1860-1861 America. My point is that the “We did It for States Rights” is just a bunch of hogwash revisionism history that tries to deflect from the real root cause - the Abolitionists were abhorred by the evil barbaric practice of Slavery, determined to end this practice in America, and the Elites in the South feared that their Slavery practice was going to end & they went full throttle into leaving the Union for the primary purpose of protecting this Slavery practice.
Go read the Confederate Constitution and compare it word for word with the US Constitution, as it was in 1860. And I’m not going to argue with any liars who try to dishonestly add anything else as a reason for the Southern States leaving the Union than this.