Here’s a religious rationale for some degree of secularism, as expressed by famous creationist Harun Yahya:
“Muslim writer and intellectual, Harun Yahya, believes that “secularism is the safeguard of Islam.” Instead, he says, of the hypocrisy of women with very little religion, dressed in long black robes, or men in white robes and long beards, we must distinguish Muslims by the integrity of their lives and the goodness of their characters. Secularism, he believes, allows those with no religion to be identified as such, whilst sincerely believing Muslim men and women are allowed the freedom to practice their faith.”
I’ve often run into the rationale that when there is no state pressure to adopt a religion, the believers you see will believe out of sincere conviction rather than just put on an outward appearance. But it’s interesting that ease of identifying nonbelievers can also be part of the rationale. I wonder if that’s because nonobservance is then more easily identified with lack of piety, and hence it’s easier for the pious to to avoid corruption due to association with the ways of the irreligious.