Most "Great Divides" are pretty average

Our fight, of [A] against [B] over [C], is but one battle in the ancient war over [F], along the great divide between [D] and [E]. Many do not realize how many of our apparently mundane conflicts are, in reality, battles in this ancient war. Today is a crucial day in this war, so we must not give up, and we must not lose hope, or someday [D] may lose [F] forever. Fight, fight! a painfully green blogger, I can't restrain myself:

First, if you have any opinions worth talking about, they will eventually develop into disagreements with others. Rhetorical belligerence may not be attractive, but at what point do you consider it a "conflict"?
People seem to derive self-worth from professing their beliefs; so if you disagree it's not simply an attack on their idea, they view it is an assault on 'their being.' Exaggerating the conflict makes it seem more important that it actually is and so gives an individual and corporate ego-boost (honestly, who cares whether you use Gentoo or Ubuntu?)
Also, people don't deal well with ambiguity; clearly defining who's "a good guy" makes you a more effective 'combatant.' Many divides are sub-issues, used as a supporting argument for a 'greater divide;' (i. e. it might be worth alienating a small number of people on your own larger-issue divide if it increases group cohesiveness in the remaining members.)

Secondly, a number of people hold beliefs (this might be too strong a term,) that they care very little about, so it's necessary to determine which divides they care about, not just what side of the divide they are on.

Thirdly, 'Intellectuals vs. Manualists' (or whatever you want to call it) isn't covered, which is strange since this is one of the oldest and most widespread "great divides."in recent history 'intellectuals' have won the propaganda war, primarily because 'Manualists' (when not allowed to eradicate intellectuals) have a very limited number of defenses, and have to confront intellectuals on their 'home-ground' to even argue with them. It's currently much cooler to be a nerd making a jock look stupid.......

1. "How is this division a key division underlying many others?"
People develop different strategies to maximize their effectiveness; it's natural that some people would think to save themselves work and that others would work to save themselves thinking........

2. "How do people acquire their sides in this conflict"? might be born a 'thinker,' or a 'worker;' your juvenile environment might reward one-type of strategy over the other, you might self-interestedly align yourself with a cause.

3. "How has this conflict lasted so long, without one side winning?"
If you take a nativist view, there is no way to change the fact that the divide exists, if you view it as cultural strategy, one could argue that diversity is (in the long run) more stable. Or you can say the the intellectuals are in fact winning, and probably will win (unless the Mayans are right, or zombies invade New York -- the center of the known universe.)

4. "How could one side finally win such an old conflict?"
Marginalizing your opponent to the point where people think that he/she/they is/are in the minority, is just about the only way to win one of these "epic struggles between good and evil." I hesitate to mention the Overton window, but cultural drift is the only way to win. (Rhetoric does not require factual accuracy; it's not actually necessary that they really be in the minority-----though it's really stupid to try this tactic against a majority-----if you are trying to bring back the worship of Bacchus, don't appeal to the idea that "everybody's doing it.")

5. Why is one side better than the other in an absolute sense?
Intelligence saves people work. Though this does not seem to be effective for people who are unable, unwilling or haven't been trained to think.

6. Why can’t those folks be persuaded that their side is bad?
Because the only people that will try to persuade them are on the other side, so in order to 'switch' beliefs, they must be convinced of 2 things, not merely that they are wrong.
Or people like to feel better than everyone else, they enjoy being entrenched jingoists, there are probably some hard-wired preferences.

7. Why can’t peaceful compromise replace conflict?
Maybe it can and has. We certainly don't burn heretics any more (in many parts of the world at least.)
Of course we could also be at the furthest reach of the pendulum's swing, and we wouldn't know.