So what do they say it is about? I can only assume that from their perspective making it "about slavery" would make white Unionists "good guys," and we can't have that! So the war "must" be about something Marxist. Am I right?
I assume you will agree that the CW was in a real sense not about slavery, since slavery was not really under genuine threat in 1860.
Rather, I think the issue was for most southerners, as they freely proclaimed, one of honor. Northerners kept saying slavery was wrong, and southerners resented it bitterly. The infamous Wigfall said something along the lines of how anybody would resent a neighbor who constantly denigrated your family, even if what he said might be true.
They got sick and tired of being told they were wrong and wanted their own country where they wouldn't have to listen to it. I truly believe this was the precipitating factor. The actual issue that split the country, expansion into the territories, was symbolic of this deeper issue.
The South was insisting that the federal government enforce slavery in all the territories, primarily as a symbol that slavery and therefore slavers were not evil, since slavery was not economically viable in most if not all of the existing territories. Northerners wanted slavery excluded from all the territories as a symbol of its evil and eventual demise.
The country could not both applaud and deride slavery and slaveowners, so it came apart.
As so often in history, contrary to vulgar Marxism, the war was not primarily about economic issues. It was primarily about issues of honor and feeeelliiings.
But the real reasons were more racist, northerners wanted to keep the new territories lily white and free from the untermensch black encroachment. Everyone knew slavery was dying and they wanted to per-empt a black invasion.
If you substitute the word "immediate" for "real," we are in agreement.
That fact that the immediate cause was the seizure of American ("Federal") property and subsequent secession of the Cotton States, along with Lincoln's conciliatory attempts to save the Union as his principle short-term goal, has caused no end of mischief with Lost Causers, who want to pretend that what was merely the latest case was the actual cause of the War.
Unfortunately for them, one has to ignore the foundational basis of the Republican Party, Lincoln's own personal history, and nearly the entire history of intra-American disputes from the 3/5 Compromise going forward to believe that slavery was not the real cause of the War. (Actually, you can go back further than the Constitution, and even before the Revolution.)
The question of Southern Honor puts me in the mind of Emerson's famous phrase: "The louder he spoke of his honor, the faster we counted our spoons..." but yes, I will concede there was a large element of that. But actually, I believe there are two other important causes that you miss: 1) The slavers (as distinct from Southerners, generally) had bargained in bad faith for years. The election of 1860 precipitated a crisis because it was now clear that the three separate parties all calling themselves "Democrats" could no longer keep a coalition together well enough to retain Federal power. 2) New York and Pennsylvania had both eclipsed Virginia as the most important states of the Union. They were both far more populous by 1830, and in the succeeding 30 years industry had lifted their ascendant populations out of poor immigrant status. The prestige and influence of the South was rapidly waning. This produced in the slavers a "crisis mentality." (Which the election drove forcefully home.)
As to rest, we agree. The Charles and Mary Beard version of history and its many variants are pathetically silly, and the fact that it was taken up by academia so enthusiastically (and its various incarnations have managed to survive despite Beard's own demise) is a testimonial to the fact that "progressive" academia is nothing very new.
Or as my Dad once put it, in reference to the wars in Iraq and Afghanistan and the "no blood for oil" idiots: "I didn't sign-up for the combat infantry on December 10th, 1941 because of the expansion of US markets into the Far East. That's all crap. I signed up because of 2400 dead guys at the bottom of Pearl Harbor, and so did everybody else."
Duty, Honor, Country, yes.
Money? No.