"The Castaways of Tanagar" by Brian Stableford (1981)
"Salvador shook his head. 'If there's to be a new cult,' he said, 'It won't be of my making, even if I remain its figurehead. Religious beliefs may have far more power to determine how people live than scientific ones, but their effect on the course of history is far less than what appearances might suggest. What alters the course of history is discovery and technology. If any man is to make a substantial contribution to the future of this new civilization then he must do it through Macaria, not Merkad. Messiahs, in the long run, have little to contribute to the pattern of progress, precisely because an essential part of progress is winning freedom from the prison of their arbitrary ideas. The kind of stable society that results from religious tyranny is a fake, because it depends upon deception and faith."
Ever hear of Brian Stableford? No? Well neither had I. He did a run of Daw paperbacks in the late 70s and early 80s, and (re)lapsed back into obscurity soon after. These days he's known more as a translator of obscure French science fiction novels, though his output remains prolific.
It's really a shame that he's not better known to modern readers, because "The Castaways of Tanagar" is a fantastic book. I can only assume that this book failed to find an audience because it was a) burdened with a terrible cover, b) given a less-than-interesting title, and c) it came across as too dense, too intellectual, or even too pretentious for readers back in the 80s.
Whatever the true cause of his fame - or lack thereof - I would encourage fans of more intellectual science fiction to locate this book. It follows the exploits of several space travelers as they return to Earth, their ancestral home, and describes the social experiment designed by their leader. Along the way the author finds time to say a lot of insightful things about our society, and the world presented in "The Castaways of Tanagar" is as convincing as something you might come across in Tolkein, Jules Verne, or even Joseph Conrad.
Yes, there are moments in the book where the author tries too hard to make a point. The description of Tanagarian society threatened to bring the whole thing to a screeching halt, but such faults are forgivable, given the well-delineated nature of both the characters and the environment they inhabit.
I would strongly recommend Stableford if you've exhausted authors like Frank Herbert or PKD. He offers a uniquely British take on the genre, and although his work is challenging, it is definitely worth your time.