Best numbers I've seen: 260,000 dead for the South. 360,000 dead for the North. Thus greater absolute numbers for the North. Significantly greater relative numbers in the South. Anyway you slice it, a horrific tragedy.
VERY few northern soldiers fought because they were forced into it. The Confederacy resorted to conscription before the Union did. The vast majority of Union soldiers were volunteers, although large numbers were probably "encouraged" to join up by social pressure, and some by bounties, etc.
Given the relative levels of education in the two sections, and the considerably freer press in the North, it is likely that the average Northerner was a lot better informed about the issues involved than the average Southerner was. It's interesting that you also seem to think that midwestern farmboys had nothing to fight about besides slvery and blacks. Take a look at a map and perhaps you can come up with other reasons why Iowa or Minnesota residents might object to the lower Mississippi valley becoming part of a hostile nation.
Hint: Jefferson said that if Napoleon got firm hold of New Orleans and Louisiana, the US would be forced to throw itself back into the arms of Great Britain.