Edit: This suggestion has been integrated into the site FAQ. Oct 1, 2011
The first "bullet point" should read something like this:
This site is to create a canon of knowledge ABOUT the subject of "Christianity." This is not a debate forum. Users do not expect to be challenged on their belief system, and questions asked under false pretense just to "make a point" or to challenge those tenets will be closed as [not constructive].
The premise was discussed in this meta post on:
Why is Christianity the only true religion?
This site's main challenge is to stay vigilant against the inevitable intrusion of "How can you guys believe this stuff?" questions and the more veiled "I'm making a point against Christianity" questions.
If you can uphold this behavior as unacceptable, this site will be huge.
Canonize this in your FAQ.