The United States overall has a very individualistic and free cutlure. Americans are reluctant to accept intervention from governmental or religious authorities. We can apply the theory of memes to explain how this attitude effects religion in America.
Catholic religious structure is very centralized and authoritarian. The individual within the Catholic religion has very little latitude for interpretation of scripture. The Pope is the final authority on doctrine.
America has a large Evangelical/Protestant Christian presence. I believe this is due to the fact that these institutions are more "open-minded" in their doctrine. Also, if a person is unhappy with one church, he/she may change to one more in keeping with their views, but still be concidered under the umbrella of "Christian". Americans like to make up their own minds and reject having rules and dogma imposed upon them. In addition, Evengelical groups have as their purpose a duty to evangelize and create converts. In a sense to "infect" others with this meme. In these ways the idea "procreates" in society.
A meme differs from a gene in that a meme that is not beneficial to a society/person may survive and propogate, while one that would be beneficial may not survive.
memes in his book
The Selfish Gene