I've heard yet more talk about the propriety of dating outside of one's religion. This talk confirms my view that people use religion not as a guide to what is true, but as a marker for other things.
As an atheist, I do not make a point of agreeing with C. S. Lewis, but I do agree that religion can be infinitely important or not important at all, but that it cannot be only somewhat important. If someone genuinely believes in his religion, why should he not want a partner who shares his values with regard to that infinitely important matter, let alone a partner who will, according to the faith, join him in heaven?
The answer, of course, is that at least in our society, most people who self-identify as members of a religion do not genuinely believe in it, except insofar as they can cherry-pick from it to confirm what they wanted to believe anyway. For the most part, people use religion as a ritual of belonging - to a family, an ethnicity, a chosen tribe, or a secular cause. Just consider the people who want to post the Ten Commandments in public spaces but who cannot name them, or the people who faithfully observe certain holy days but who are effectively apatheists the rest of the year.
If we were honest, we should pay less attention to religious affiliation than we do, not more. The fact that one person goes through the motions on Ash Wednesday and the other does so on Yom Kippur should have no more significance, and arguably much less, than different socioeconomic backgrounds.