Stephen Prothero explains partly why discourse about religion in the United States is so poor (and charged):
The religious right argues that religious literacy goes away in the early 1960s because of the Supreme Court. The Supreme Court bans devotional Bible reading and prayer in public schools in 1962 and 1963, which critics argue essentially exiles God from public schools so that they are now religion-free zones. Now, children grow up not only without a reverence for God, but also without an understanding of the Bible and Christianity. The argument I make about religious literacy is that the story actually begins a century earlier. The villains are not secular people in the Supreme Court but actually religious people. It is caused by the Second Great Awakening and the replacement of Puritanism by Evangelicalism as the dominant religious impulse in the country. Before the Second Great Awakening, there was always this conversation among Christians between the head and the heart, trying to get a religion that was both intellectually sound and emotionally resonant. But with the Second Great Awakening comes this new form of religion that really prioritizes feeling and emphasizes loving Jesus rather than knowing what Jesus had to say. This is when religious literacy starts to go away. It doesn’t really matter much what Christianity teaches, what matters is how it feels to be in a relationship with Jesus. Simultaneously, as you have that shift from knowing the doctrine of your tradition to feeling intensely about God, there is a shift toward morality where the focus of the tradition becomes making the society more Protestant by using voluntary associations to get rid of slavery, to make the schools better, to improve prisons. In order to do that, it is important for people to downplay denominational differences. You don’t really want to bring up the distinctions between Methodists and Lutherans because you want both denominations to work together to get the Bible printed and distributed or to do the work of the American Tract Society. So that also pushed people away from conversations about doctrine. As the theology side of religion starts to go away, our collective memory starts to atrophy. That really happens over the course of the nineteenth century.
And it continues in the twentieth.