Why, people often ask, can't conservatives and liberals just get along? Why can't they be more civil and courteous, like they used to be? Why can't they reach compromises instead of seemingly refusing to agree on anything? To answer those questions, allow me to ask another one: why couldn't politicians from Northern and Southern states reach a compromise on the issue of slavery back around 1860? Why did there have to be secession and civil war?
Here's a theory: there are some issues that can't be resolved peacefully and amicably, because the stakes are so high that neither side can afford to lose the debate. The difference between the two positions is so great that it becomes a winner-take-all contest. For example, you can't say 'slavery is OK if slaves only have to work three days a week' or something like that. And these intractable issues are basically philosophical ones for which there is no scientifically demonstrable correct answer—again, like whether slavery is right or wrong. The two sides aren't interested in figuring out who is right and who is wrong in a logical and dispassionate manner. Better to be wrong but win than be right but lose. Issues of this sort seem to come about every century or so, and even our carefully designed system of government can't handle them, so we resort to violence. This was what happened in 1861 and might be happening today as well.
As we all know, the American Civil War was caused by the issue of whether slavery should remain legal, and the related issue of whether states could secede from the union. Or was it? I suspect that the one question on which there could be no compromise was more like 'Shall blacks continue to be considered as obviously and undeniably inferior to whites?'. For white southerners, at least, this was a question on which only one answer, an unequivocal 'yes', was allowable. Because while most whites in the South were not wealthy plantation owners, and most owned no slaves at all, all benefited from a system which effectively defined them as superior to blacks. 'I may not be much' a southern white man could tell himself, 'but at least I'm not black'. Americans need a source of self-esteem and self-worth--we need some sort of evidence that we have value, because without it we often times don't feel entitled to happiness. Our ethos tells us that happiness doesn't just grow on trees, no, it must be earned. So, in a sense the issue in 1861 was whether Southern whites were entitled to the happiness which they derived from a sense of superiority over blacks, and the possibility that slavery might be abolished some day threatened to take that away. Nobody phrased it that way in the newspapers of the day, because they didn't fully understand it themselves, but that was the basic issue. And it was an issue important enough to fight and die for, because there is nothing more precious than happiness. It had gone without saying since the country was born (and even before) that the proper place of blacks was as subservient to whites. When an assumption as basic as that comes into question, the result is liable to be a dispute so bitter than it can only be resolved by means of violence.
What then, is the basic issue behind today's culture war between conservatives and liberals? Perhaps another assumption which has largely gone without saying since the early days of the union is now coming into doubt. Namely, the notion that the USA was created, possibly by will of God himself, primarily for the benefit of white Christians of European descent. You may recall from school the concept of 'Manifest Destiny'--the 19th century belief that surely it was the will of God that the vast hinterlands of America had been set aside for such people. It was okay to take the land from the natives since God had effectively authorized it. For most of our nation's history whites composed the overwhelming majority of the population. But the share that is comprised by other ethnic groups is growing considerably nowadays. There has been a lot of immigration from all over the world recently, and white Americans have a relatively low fertility rate. Baring a radical demographic change, within a few decades less than half of all US citizens will be white. The result has been a growing sense of anxiety among some white Americans, especially conservatives without college education. Perhaps a sense of being the chosen people of this land gives them a feeling of self-worth and happiness, just as a sense of being superior to blacks did for antebellum southern whites.
Suppose that in 1861 the southern states didn't secede from the union—there was no need to do so, because none other than Jefferson Davis had just been elected president of the USA as a whole! An obscure candidate named Abraham Lincoln had been knocked out of the running early in the election campaign, and the new Republican party had ultimately put forward an uninspiring and unpopular one. With the choices for president as meager as they were, many voters felt there was little point in voting at all, and the Electoral College had allowed Davis to win with a minority of the popular vote. Once in office, it became clear that he had no interest in reaching out to anyone who hadn't supported him during the election. Davis, of course, was a staunch believer in the attitudes towards the races that had been in place for centuries, and was fiercely resistant to change, even though more and more Americans were moving in that direction. His goal was entirely to reshape America to reflect the wishes of the southern states alone, and to make certain that it would remain that way for as long as possible even after he had left office. The claims he routinely made--for instance about blacks being dangerous and untrustworthy people who would rape and murder whites if given the slightest chance--were absurd to the majority of Americans, but he clearly did not care. He was not speaking to them. The bulk of the people resented this state of affairs, but due to widespread gerrymandering and political corruption they were effectively unrepresented and powerless in Washington. Southerners' on the other hand, were delighted with the Davis administration and considered it to be a vindication of their beliefs.
That, if you haven't guessed it already, is basically where we are today. When an issue comes about which threatens to redefine the very conditions under which Americans feel entitled to a sense of self-worth and happiness, then any change will be fought tooth and nail by devotees of the old system. It is useless to try to reason with them or to expect them to compromise. Whereas the rest of society has already changed its mind on the matter (and doesn't consider it to be nearly as important), there will be those who cannot tolerate a change and will do whatever they can to prevent it, even if it is already too late to win.