That a very minor risk. The Civil War wouldn’t have happened without slavery which was the reason the Southern states became more and more alienated from the North and was the reason their culture and economy were so different and was the source of their various conflicts. Calling the Civil War righteous (which is a bizarre way of framing it) has nothing to do with the reasons why the South seceded and attacked the North. The North’s response to secession and military attack was pretty much what you’d expect, and wasn’t about slavery, but about States breaking from the Union and waging war against US troops. So it’s really simple to say that the root cause of the war was slavery. While there were other minor grievances or differences (State’s right’s being the weirdest, since the South’s strangle-hold on Congress and successes in controlling the Feds. was effectively depriving the Northern states of more rights than the reverse), without then there would still have been a eventual major conflict under the circumstances based on the divisions slavery caused. That in no way suggests that the Union was just in how they waged the war or that it was “righteous.” Even if there’s a risk of people assuming the Union were fighting to end slavery, it’s still preferable that the simple truth that the Civil War was about slavery is abundantly clear, since it’s only after that’s made clear that the reality of the conflict can be understood.
Suggesting the Civil War was not fought over secessionists fighting to preserve the institution of slavery they felt was threatened, but over their other differences is like suggesting that WW II wasn’t started by Germany invading Poland, but by German trade disputes with Britain and France.