Could it be that some people are just really sensitive when it comes to logically defending a very emotionally charged subject like a belief system?
Scully,
I think alot of times what you said is the problem, people paint themselves into a corner from a logical/debate standpoint and the shouting begins. But there are times that I think there is something else at work.
People always claim that believers get upset because their beliefs are being attacked with unassailable logic etc, and as I said above that is often the case, however there are times when I think believers are upset because of what they percieve to be extreme disrespect. If they are believers and truly love their object of worship/belief system they are none the too happy to hear someone deride, sneer at, launch profanity at, etc. their object of worship/belief system. It upsets them because something the cherish is being disrespected, the analogy would be I guess someone launching a vicious verbal attack on a loved one in your family. Logic has nothing to do with that, its about respect, someone calling your mother for instance all sorts of deplorable things will often incite people to violence, much less shouting. Its one thing to say that you don't think very much of one's mother, its quite another to call her a lazy whore.
Faith and beliefs aren't about logic, just like love for a family member isn't about logic, it just is. So there are times that I think that is what is upsetting to people that love God, Jesus, whatever, they feel like, you don't want to believe in, worship them, fine, but don't disrespect them to a believer.
Also, just my 2 cents.