When I teach Civil War, I offer five probable options as to cause:
Irrepressible conflict, slavery, sectionalism/nationalism, and competing economies. That said, I announce,"You have paid your money. Now take your choice. Personally, I favor irrepressible conflict as will most people who pass this course."
But it looks like you're playing a slippery game. You say: "Sure. Don't get me wrong, its my opinion that slavery was the fulcrum, the prime mover." And then, 'But I think its fairly meaningless to use the criteria of "the war would not have happened if"....as the determinant of causation. I would posit that if the program of industrialization and resultant immigration in the north had not occurred that northern sentiments would have been damped as they had been for decades before living with slavery as a neighbor. Thus no war and no secession. Just because I believe this is true does not lead me to say "industrialization and immigration is the ultimate cause."'
If something is "the fulcrum, the prime mover," it's likely that the event caused couldn't have happened without it. Of course any unique event results from a particular combination of unique events, but it looks like you are trying to equate various kinds of causes and not distinguishing between those that are more and less important.
According to Aristotle there are formal, material, efficient, and final causes. Something like state's rights may be a formal or material cause -- part of the general situtation that made the war possible -- without being an efficient or a final cause. Industrialization, and the invention of the cotton gin fall in a similar category. They helped to make possible secession and war, but they seem to be more contributory than primary factors. "Fulcrum" can be a pretty slippery term, but if slavery was in some way "the prime mover" that means it was more important than other contributory or secondary causes.
Discussions here tend to focus more on guilt and sin, good and evil, purity and impurity, rather than on what happened and why. Very often people are trying to get a "directed verdict." They assume that slavery was wrong and the South couldn't have been wrong, therefore slavery couldn't have been an important part of what the war was about.
So these discussions tend to be of limited use as history, and we get long pointless arguments about whether the war was "all about" slavery or not. If you recognize the importance of slavery, then you can also admit the significance of other factors without playing the chump's "it was all about"/"it wasn't all about" game.