Yes, you're right, everything is grey and meaningless, the north had no redeeming qualities that made it inherently superior to the south, the cassus beli of being entitled to own other human beings because they are biologically inferior was just as valid, and the only reason the union went to war was for material realpolitiks reasons, despite the 30 years tension lead up to the war being entirely about the issue of slavery and the war itself about the issue of slavery. The mealymouthed political speeches about preserving the union being paramount weren't just about placating the southern state governments without enraging their constituents who, obviously, didn't support slavery as an instution at all and didn't see it as an integral part of their cultural identity. That's why the emancipation proclamation never happened, because once it was clear the north was going to easily win the war and the southern states still would not surrender, the north had absolutely no incentive to abolish slavery at all. After all, it was all about punishing the south and money, so slavery was not a target.