First of all, thank you for that thoughtful and thought-provoking essay. I think shifting the focus away from slavery as an end in itself would be a good thing.
Slavery was (is) in itself a moral issue. It is in that sense that it is an end in itself for many who look at the Civil War.
Slavery was (is) also an economic issue that is infused with morality. It is the ultimate expression of some people using others for monetary gain.
Some people using (‘employing’) others for monetary gain is the basis of capitalism. Thus, as the intellectual and political leaders of the South recognized, Marx’s “wage slavery” is a real thing: like bondage slavery, it is some people using others as machines — or draft animals — for monetary gain.
So the South was fighting against capitalism — wage slavery — as consciously as it was fighting to preserve bondage slavery. That cuts both ways, though: the North was fighting against bondage slavery to ensure that the whole nation would be subject to the economic imperatives of wage slavery.
So our Civil War was an armed conflict between bondage slavery and wage slavery. To view it as a war in which one side was for slavery and the other side was against it is exactly what the beneficiaries of that war wish us to do.