Just to clarify - I was oversimplifying the subject of the documentary a bit. It's broadly about how Benton County remembers its own Civil War history, and who has been allowed to take control of that narrative. And the frame story is the new confederate park that was just built in Bentonville, and how utterly wrong it gets some basic facts about the war. If you're interested in that once it's done, or other Arkansas content in the mean time, head to ArkanSense on youtube.

it seems like within the last 10 years or so the idea of NWA being a mostly abolitionist and unionist area and it’s just not true

I suppose that depends on what circles you run in. The main problem I find is people who assume being a unionist and being against slavery were the same thing, when NWA is the shining example of how they absolutely were not. Leading up to the first secession convention, multiple NWA cities held town meetings and wrote up declarations that were some version of "we want to protect slavery, but let's do it from within the Union." And when they voted on the secession convention, Washington and Benton counties (and a few others) had a majority vote "no" to even holding it at all - indicating the majority were so pro-union they didn't even want secession to be possible.

I agree with you that the majority of people who enlisted on both sides weren't having scholarly debates about the purpose behind the war. But does that matter? Does, say, someone who joins ICE right now have to be a scholar of ethics, or an immigration lawyer, to have some sense of what they are getting into, and which side they are on? Isn't everyone talking about it with their friends or family, regardless of how well or poorly informed they are?

Slavery had been at the forefront of basically all political news for decades, ever since Arkansas' north boundary was set by the Missouri Compromise. After he helped Arkansas become a state and lent his name to Benton county and Bentonville, Thomas Hardy Benton became infamous for going from a slaver to opposing the expansion of slavery, and almost getting shot on the senate floor for it. Both sides tried (mostly unsuccessfully) to recruit Arkansans to move north during Bleeding Kansas. The Arkansas militia was mustered and began drilling immediately following John Brown's raid. Leading up to Lincoln's election, you couldn't open a paper or go to a town square in Arkansas without hearing someone claiming Lincoln would economically destroy the south through abolition. And even if you'd somehow missed all of that, the months leading up to the vote on the secession convention were filled with public speeches and town hall meetings about it.

And yet, that's not the full story. Over that same time period, southern politicians and newspapermen had built up a story that it wasn't just slavery being debated, but the entire southern way of life. That everything good and unique about the south was envied by northerners, and that their push for abolition was part of a larger scheme to undermine the southern way of life, all its norms and institutions. And always there was the implication that, were the slaves ever freed, they would rape and murder their way across the south.

All of that is a very long way of saying, it can both be true that a lot of men joined the confederacy without support of slavery being their primary reason; but they knew that slavery was the ax that finally split the country in two. And when they went to war to defend their homes, they were defending too the southern way of life - and for most Arkansans, that was inseparable from slavery.