This was before the Jimmy Swaggart fiasco, am I right? I think stuff like that turns the people off religious types.FOM, all I can say is that in the mid-'80s, having a major character on a hit TV show suddenly announce she was an atheist was a HUGE deal. A very, very different time from today. Jerry Falwell and the "Moral Majority" were in full flower. A presidential candidate's religious views were a big part of how he (always "he" back then) would be viewed by voters. The public practice of religion was an enormous lever and force in American society. There would be zero public benefit in such a thing. And, as we've noted, GGC and the writers seemed to do this to CS at numerous points during the show run – introduce behaviors and traits to Maddie that they knew would be unpopular and make people like her less.
I always believed that having Maddie doubt there was a God was just a plot device so they could have one of their great debates while toying with the audience's possible expectation of David being the atheist/agnostic. It did fit with Maddie's character, though. While David was the more streetwise of the two, Maddie was always the more cynical one.