Good science fiction authors are at the same time remarkably prophetic in their thinking and humorously influenced by their own time. I remember laughing aloud when one of the characters in Heinlein’s Stranger in a Strange Land began darning a sock. To me, it was hilarious that in a futuristic world with space travel, characters would still feel the need to repair old socks. It could have been the intention, but it seems like at the time it was considered the kind of basic activity that one would do as part of household life. Now, in 2009, we still don’t have space travel, but we toss our socks out as soon as they get a hole. Go figure.
One thing many authors seem to underestimate, from greats like Arthur Clarke (Hammer of God) to modern authors like Kevin Anderson (Saga of Seven Suns), is the ability for religious texts to maintain their continuity over time. Books like the Koran, Torah, and Bible have remained largely unchanged for roughly two thousand years, even as the interpretations of their contents and the organizations surrounding them redefine their beliefs and suffer large-scale schisms.
Unlike many other books, when people believe a text has the keys to living a better life, they are more inclined to preserve it. Many scifi novels feature exotic fusions of different belief structures, but I think that in reality, this outcome is dubious. It is not something we’ve really seen in the past several thousand years, so I think it is doubtful for the next thousand as well.
What I think is more realistic is the struggle to apply a set of beliefs to a rapidly changing and technological world filled with electronic miracles. I think Richard Morgan was able to capture this in his book Altered Carbon, where the Catholic Church refuses to allow its members to be digitally resurrected after death and downloaded into a new body, feeling that to do so violates a realm of existence that should be governed by God.
If you read the appendicies, Frank Herbert has done something similar in Dune on a wider scale. While his story does feature religious “fusions,” he explains how they were formed as a resolution to extensive religious wars over the creation of true artificial intelligences, or “thinking machines.” Even after years of discussion, the resolutions decided upon were largely rejected by the population, and the clerics who worked to create it often ostracized or killed by their respective churches.