I'm glad Ridley has finally tackled what, to me, is the toughest issue humanity will face on the whole first contact issue....namely, the impact the existence of aliens will have on organized religion. The only other movie I can recall that kinda sorta flirted with the concept was Contact, the film based on Michael Crichton's novel; but it wasn't a major part of the movie. In Prometheus, it's the central issue.
The mere existence of aliens would create profound questions for long-established dogma of religions like Christianity, Islam, Hinduism and Buddhism. Where do aliens fit in the Bible, or the Koran? Do they believe in God/Allah/Brahma? Do they have a religion of their own?