It occurred to me a little too late that I conflated the southern states' reasoning at the time of the Civil War with the after-the-fact reasoning of those who support the "Confederate cause" overall. Of course, the interstate commerce decisions came much later and weren't in play at the time of the Civil War. Still, I do think the reasoning was disingenuous at both stages. The Confederate states rebelled primarily because they wanted slavery and institutional racism. If you read the Declarations of Causes by the Confederate states in support of their secession (link
http://www.civilwar.org/education/histo ... auses.html), most of the declarations mention slavery pretty heavily. While many of them do mention states' rights as a broader issue, it seems pretty clear from the context which of those "rights" they were willing to go to war over. Further, the Confederate states appear to not mention very many grievances other than interference with slavery.
In fairness, I haven't read these declarations in their entirety, so as before, feel welcome to "CMV."