The big problem for him is his entire argument falls apart when the confederacy openly admits in their articles of confederation that they're fighting to keep slavery. If the Union wasn't fighting them over slavery, apparently the confederates didn't get that message. How can anyone make an argument that the war wasn't over slavery when it's literally written in their constitution that they're fighting to keep
They say this because long after the civil war you had impoverished white people working in plantations alongside black people across the south. Capitalism is really ugly and doesn't discriminate if you look at all of it.
Civil war was over slavery. But at the end of the day, if a poor white person wanted to eat/survive, if they weren't elite or had connections, they had to pick cotton and tabbaco for shytty wages as well.