Generally, this is an unspoken rule used on the internet. Regardless, the unspoken rule is broken and being the internet, people are easily offended.
I'm referring to the discussion of religious beliefs (and non religious) on the database. It goes without saying that these debates never end well even if the intentions are harmless. It would be a good idea to include something regarding religious debate in the chat rules and on the rules page. It doesn't happen often, but it would be nice if it wasn't to happen at all.