I have to point out you aren't disagreeing with him, but with Confederate founding fathers who made it clear in their secession documents of 1860-61 that they were seceding mostly over the issue of slavery.
They quote part of the 1852 secession ordinance in the 1860 secession declaration. That gives it weight and meaning in 1860. I do take these men at their word, which is exactly why I know there is more going on than just slavery at a motivation. What I do not fully understand is why you and others like Unionblue can't see the other reasons alongside slavery.