All history is debated time and time again. I read a book called The Apostles of Disunion that showed many states that were rabid secessionists sent emissaries to less eager states to give firey speeches to fan the flames of Secession. Interesting read. I had never pondered the freedom/slavery connection until I read the Foner book. After examination, it really fits. The book also examines how the perception/definition of freedom has evolved throughout our history from Colonial days through modern times. It's a heavy read that requires effort to truly absorb the totality of the subject. I wouldn't necessarily call it a recreational read, but if you are interested in the interpretations of freedom and how they have evolved in America, it's a must read, imo.
And I don't disagree with you. I just think that it's a combination of slavery and how freedom is perceived in relation to slavery in the North and South. I feel that one can't argue the slavery cause without considering the freedom issues and vice-versa. They are completely intertwined, imo.