Little more complicated (but also less complicated at the same time, somehow) than that. A lot of it also had to do with the inevitability of the United States moving away from slavery as an institution. The Missouri Compromise effectively prevented any further parts of the remaining Louisiana Purchase territories from entering the Union as slaveholding states. The Dread Scott decision overruled this in 1857, but by this point the damage was done and animosity between the two halves of the US was coming to a head. To add to this, Alexander Stephens and others very publicly called for secession on the basis of preserving slavery as an institution. See Stephens' "Cornerstone Speech" and the various declarations of secession made by the former Confederate states themselves for additional details. So, taxes were possibly a component, but the core driving motivator behind secession was in many ways more fundamental. One could even argue that the taxation argument is a way of whitewashing what is fundamentally a motive for the preservation of slavery, as the Revolutionary War was fought on the basis of taxation without representation and the Confederacy wanted to draw explicit parallels to their secession and the United States' secession from England, however specious that comparison might be.