As far as I'm aware, the GenOT mods tried allowing it once, and it didn't work out. Religion is simply a topic where people easily take statements the wrong way and get offended. Keeping such a thread constructive would be an enormous task, and we don't really think dedicating a whole mod team the size of the current one to these threads is worth it.
<Note: Post made from personal, anecdotal experience. Post reflects my personal view, not the view of the moderation team. Post may contain slight exaggeration.>