Americans, as a whole, are tempted to oversimplify matters, especially when it comes to issues of philosophy and religion. Before Western religions came to America, there were many complex rituals that were taken to heart by Catholics and Protestants - strict adherence to Lent, long and dedicated studies of the Bible and its teachings, and more. However, with the religious movements in America, there seems to be a lowering of standards as to what constitutes true religious and philosophical thinking. This oversimplification leads to a relaxed notion of how much critical thinking and scholarship goes into religion and philosophy, opting instead for easy answers and comfortable notions of community and fun without the intellectual work that often goes into this kind of thinking.
Much of this has to do with the increased accountability and responsibility that comes with complex issues and tenets of faith. In short, making things simpler is easier, and people like things when they are easier. The Puritans, for example, had extremely distinctive views on how clerics should dress and very different ideas about the episcopal system than did Catholics and Protestants in their various denominations. This, in addition to their much stricter and less permissive view of life and morality, made their religion an extremely unpopular one that did not catch on with a substantial number of the American population. While they enjoyed great successes in England the 1600s, many Puritans in America were of a much stricter and more radical denomination, banning the celebration of Christmas in 1659 in Boston. The banning of secular and leisure activities on moral grounds also made it a far less desirable religion than many Americans were willing to deal with. Due to their adherence to their beliefs, which were often restrictive, Americans did not see it as simple or livable enough of a religion to adhere to.
The need for a simple answer or methodology regarding religions or philosophies may be rooted in deep-seated nationalism and individual pride that many Americans have about their country. America is a proud nation, and rightfully so; it has accomplished a great deal in its comparatively short existence. However, as people increasingly define themselves by their national origin and that status goes unchallenged for so long, people may take it as a given that they are already on top and do not need to strive to do better. As a result, they do not engage in activities that intellectually challenge them; shortcuts are constantly taken and goalposts shifted to make things easier, like the loosening of restrictions for how much Biblical scholarship a pastor has to go through in order to counsel and advise people on matters of faith. It is entirely possible that someone who is merely active in the community, and not necessarily someone well-read and taught by Biblical scholars, could just impose their potentially flawed and personally-biased perspective on others. These people, assuming that their pastor is an authority on the Bible without having any proof to support that, may mistakenly place undue weight on their advice and take it, for lack of a better term, as gospel.
This kind of oversimplification is made into fairly clear allegory in A Canticle for Leibowitz by Walter H. Miller Jr. The "Simplification" is a phenomenon that occurs after an apocalyptic event, the goal of which is to stamp out all intellectual and scientific thinking, even to the point of persecuting those who could read. The point of the movement was to make sure no one could become smart enough to create weapons of mass destruction again; this echoed the anti-intellectualism that was happening at the time of publication. In essence, a lot of complexity and knowledge is sometimes considered to be dangerous, as it challenges established notions of what people believe and hold to - ideas which they will ardently keep even in the face of overwhelming evidence to the contrary. This kind of allegory is particularly prescient when applied to America, where messages and religions are simplified in order to reach the widest possible audience, who want to be instantly gratified and want answers to the universe without a lot of effort on their part.
Americans, and American religious groups, are prone to oversimplification in order to assert their own authority. By keeping matters as casual as possible, and requiring little scholarship or work in the pursuit of their faith, they allow themselves to move the goalposts of their religion as much as possible since they do not have to adhere to a strict set of rules. Like the Simplification in A Canticle for Leibowitz, Americans often move toward a culture of anti-intellectualism, as the opposite involves a lot of hard work and accountability that it is much easier to simply ignore. Instead, religions and philosophies require much less scholarship and critical thinking than they used to, and previous religious rituals (Communion, etc.) are simplified or relaxed in responsibility.
Miller, Walter M., Jr. A Canticle for Leibowitz. 1960. Print.