“And yet that’s exactly what thousands of them did.”
I actually think that constitutes demonizing the southerners.
Would you go to war solely to protect slavery?
No.
The real question should be directed to the Confederate leadership; would they send other men to war to protect their slave property? The answer to that was 'yes'.
Would you go to war to protect feudalism? Or to save the Tang dynasty?
Of course, you or I aren't going to go to war to save something that is not a part of our world.
If slavery was a part of our world -- if it was a part of our "way of life" -- we might go to war.
But the decisions about war for this or that reason are made higher up. A 20 year-old wasn't going to consciously decide to go to war for slavery -- though plenty did for the "Southern way of life" -- but might well fight in a war that was caused by conflicts about slavery.
FWIW, Alabama, Mississippi, and Arkansas, like Indiana, Illinois, and Iowa, had been sparsely settled a generation before. It wasn't uncommon for someone to start out with little, acquire land, build a fortune, and become a major slaveowner.
Why do you think the expansion of slavery was such a major issue. One reason was Southern pride. Another was the hope that one could become a big proprietor in the frontier territories. Maybe the hope was misquided, but that's where pride took over.
To be fair, the southern soldiers were far more conscripted than the northern soldiers.
It wasn’t so much that the southern soldiers were supporting slavery, as they were victims of the slave system.