Yes, it is important if there were practically no slaves in the North and this point is far from proven.
Why was there the underground railroad and Harriet Tubbman? Why were slaves escaping to the North?
Are people going to actually deny these historical facts?
If one is trying to say there would have been a civil war if slavery did not exist, I don't think historians will agree. They largely say the civil war was fought to end slavery. Nowhere is this clearer than in States like Missouri and Kansas where abolitionists fought.
Why are they even called Abolitionists and Jayhawkers from Kansas.
There are two subjects of contention as to the cause of the Civil War and the reasons for fighting. The immediate cause of the war was undoubtedly slavery. Period. Tariffs were not the issue. Examination of the Ordinances of Secession and other documents and statements from the seceding states make it pretty clear that slavery was the overriding cause of secession.
However, that doesn't mean that everybody who fought for the South was fighting for slavery. I would guess a very sizable pct. of Southern fighting men were fighting for other causes. Very few average Southern soldiers had slaves.
But even a number of the generals who owned slaves, like Robert E. Lee, favored emancipation. Patrick Cleburne was another Confederate general who favored freeing the slaves and enlisting them to fight for independence.
After reading quite a few books about the war I've come the conclusion that many Southerners simply were fighting because they felt they were a separate people from the North, and they didn't like Northern soldiers entering what they felt was their country and trying to enforce the rules of a separate country.
I doubt many of the average soldiers were arguing for states rights, tariffs, slavery, or other causes. I think it was an "us vs. them" kind of struggle for most of them. When most of your family, friends, and neighbors are fighting for the same side, I think the tendency is to agree and fight with and for the people you know and love. Which is basically the reason Lee rejected the offer to command the Northern army. He couldn't bring himself to fight against the people whom he loved and were closest to him.