'Must' is a bit much in a forum like this.
Funny, that. You've obviously not participated in any atheists vs Xtians threads. :D
That is the angry atheists' credo on this DB, and seems to be accepted in the 'belief' discussions. It's not my style, but other atheists vehemently demand that Xtians adhere to it. Of course, this thread is only a debate about legalistic and ethical matters, so I guess no one should require that links and explanations be provided.