Yeah, I keep hearing this, and I just... saying things happen because people are too dumb to see their own self interest is... it's just really unsatisfying. It fits the data, but it also tastes like the other times in my life where I've been wrong because I'm arrogant.
It's also unsatisfying because it's not particularly predictive; it doesn't tell me which elites the masses will follow and why.
There's also the trope of the bonding that takes place within smaller military units that makes them committed not to the cause but to each other.
In addition the other side of people too dumb to see their self interest, I am not saying these people are dumb but we see that today if we turn on the news to see for one example - farmers rationalizing themselves being hurt by retaliatory tariffs on American farm stuffs - they seem cognizant of the problem, aware of the higher order consequences for themselves, and willing to accept them to try what seems to be on some terms a way to attempt for fair trade with China, and still support the President. It may be rationalizing but it's not done out of ignorance or stupidity.
What you are asking for in the end sound like some equivalent to Psychohistory in Asimov's Foundation, which would be a neat idea.
John Brown was one of many anti-slavery militants who was involved in Bleeding Kansas, and far from being the extremist he's portrayed as today, he was widely considered a hero in the North, with songs being sung in his honor by Union troops during the war, (https://en.wikipedia.org/wiki/John_Brown%27s_Body). Others defied federal law in attempts to free slaves and secret them north towards Canada.
The resolve and radicalism of the abolitionist and free-stater movements shouldn't be underestimated. Many Americans in the antebellum years perceived slavery as an unconscionable evil just as we do today. A few undertook great personal risks to resist it, while many, many more worked through the political system to resist slavery.
Many of our contemporary perceptions of antebellum America are somewhat biased by the historical revisionism of neo-Confederates.
Even today there's no popular campaign today to go to war against Iran or North Korea, but it sure is popular in some conservative think tanks and with our current NSA, John Bolton, it's been his obsession for the last 20 years it feels like.