This week I went to a talk at Harvard by Jerry Coyne, author of Why Evolution Is True. His presentation on how various kinds of evidence support the theory of evolution was excellent, but at the end he wandered a bit to explain why so many Americans reject evolution. He said that this is because of religion, and that America is a highly religious country because it's "dysfunctional" (by which he meant things such as income inequality, drug use, and incarceration rates). The first part is unquestionably true, but the second shows a lack of understanding of our history, whether or not you think we're dysfunctional.
America isn't just a strongly religious society; in different respects, it's one of the most religious and one of the most secular countries in the world, and it's the strains between the two which explain why religion has taken on particularly disturbing forms.
The conflict goes back a long way. Massachusetts was founded by Pilgrims and Puritans, who wanted a strongly religious society. Shortly after that Roger Williams broke away and founded Rhode Island on strong terms of religious freedom. The Colonies were founded on a patchwork of religious beliefs, often by people trying to get away from the domination of other beliefs.
If the American Revolution had taken place twenty years earlier, the US might have had a very different government. That was the period of the "First Great Awakening," a period of strong evangelical activity. But key writers such as Jefferson and Paine held a very different view of religion, one of a less hands-on God, with serious doubts about parts of the Bible. The result was a tradition of separation of church and state and explicit Constitutional prohibitions against establishment of religion and violation of religious freedom.
In the Civil War and the debate over slavery which led up to it, both sides vociferously insisted God supported their cause, yet Lincoln was one of the least religious presidents, at least in the traditional sense.
The school prayer and abortion decisions of the Supreme Court sharply checked the power of religion in government. The religious conservatives dug in their heels against this, often distorting what the rulings actually said (e.g., claiming that students were forbidden from praying).
At the same time, the welfare-state, big-government advocates had successfully grabbed the term "liberal" for themselves. This led to the identification of "liberal" in the sense of being scientific, enlightened, and tolerant, with "liberalism" in the sense of expansion of the government into ever more aspects of our lives. This helped to create the impression that intellectual liberalism was a political threat. Religion has been pushed out of many aspects of popular culture; going by Hollywood movies, you'd think religion plays a rather small role in American life. Religious culture is still very active, but it's in a niche of its own. This contributes to a sense of being under siege.
With a mindset like this, intellectual issues can become symbolic threats that are more important than actual ones. Ways of teaching history have often played this role. Evolution is one of the most important because it's a symbol of things working without divine guidance, of a world where God isn't needed. Evolution and the big bang theory don't strictly imply that there isn't a God, but they do leave Him effectively unemployed. This isn't just a blow against evangelical Christians' religious beliefs; they see it as a blow for forms of social organization which they abhor. They barricade themselves behind bizarre Biblical literalism rather than concede a point to "liberals."
The way ideas influence history is complex and fascinating.