I think one of the biggest things that people need to realize is that there's knowledge about Christianity, and then there's knowledge. By this I mean, most Christians can tell you about the basics of their faith. There is a god, he had a son, born of a virgin, twelve apostles, etc. For them, that's enough. In much the same way, most people can tell you how their car works-ie, you stick the key in the ignition, turn it, and the car goes-assuming there's gas in it. For most people, that's enough.
Then there's knowledge. By this I mean the stuff that you have seminaries for, theologians like RC Sproul-deep stuff. Stuff like we talk about online. Most Christians for whatever reason don't get into that. Not because they're necessarily afraid, but because, to them, it doesn't matter. They know God loves them and wants them to be nice to each other. In the same way, most people probably couldn't tell you every little detail about how their car works, the theories behind it, how to repair it, etc. Again, it doesn't matter. If it's broke, they take it to a mechanic. If a Christian has doubts, he takes it to his minister (who, we hope, has at least some theological training).
For the most part, the Christians I run into are like that. They know the basics of their beliefs, and they're content, and, for the most part, they're fairly decent people. Should they question their beliefs? Maybe. Should we confront these guys? Not really. They are, for the most part, harmless. My mother-in-law is one of these, and she's good people.
What's unfortunate, however, is that there is a group of Christians that exists in between the basic believers and the theologians. They're the ones who've attended a bible study or a prayer meeting, and, unfortunately have more zeal than wisdom. They dive into the fray with people like us (the skeptical ones), and think they can do battle. Speaking from personal experience, I can tell you how disheartening it is to go into a thread, post what you think is a dazzling argument, only to have it shot down because (and I quote) "that obfuscation has been refuted already." I was so disgruntled that I had to look up what obfuscation meant.
In my case, I learned (over time) to actually study my arguments before posting them, and to pay attention to what had already been said on both sides. That, coupled with the shocking realization that there were times when my church cared more about appearances than helping others, eventually led to my being an atheist.
What I guess I'm saying is that it's not so much ignorance that we face from Christians (especially those that post online), it's inexperience. Don't get me wrong, I've met online and chatted with some really intelligent, thoughtful Christian posters. Unfortunately, those guys seem to get less of the limelight than the newer guys that crop up and say, "The Bible says it, I believe it, that settles it."
Marc