Two answers to stuff like this:

1. What did the Ordinance of Secession or Declaration of Causes (and related documents) actually say? Have them pull up the language of literally any one and search for “states rights” then “slave.” Hint: you’re gonna find one but not the other.
2. Knowing more about the revisionism is very useful as is knowing when it’s a waste of your time.

Edit: sorry about the Battlefields link; it’s the easiest aggregate of several even if it also tries to support the states’ rights argument by talking about laws while excluding it was all about laws regarding slavery.