I noticed this thread and had some thoughts and questions on this subject
(1) Christian members are often treated rudely on atheist forums.
I agree with your 1st conjecture and have experienced that myself. However, I have also experience this on Christian forums as well. The rules instituted over the years have helped to make dialog a bit more civil
(2) Non-Christian members are almost always censored on Christian forums (including this one).
I thought they were only censored from inter-Christian threads and they were open debate apologetically. Is that supposition incorrect?
(3) Christian forum members seem to dislike atheists. Several times I've been encouraged to label myself an an "agnostic" or a "seeker", because I seemed too reasonable to be an "atheist". After changing my label on this forum from "seeker" to "atheist", I seem to have experienced more strict enforcement of rules, suspicion of my motives, etc.
I would disagree with such a sweeping conjecture. Of course there are differing personalities and probably a lack of patience and benevolence on both sides with respect to some persons. However, I do not consider atheists my enemies and I sincerely pray for them and desire for them to have the knowledge of God in their lives. While I do tend to be careful in dispensing the pearls of the kingdom with those who have little to no appreciation of the spiritual values I hold dear, hopefully I do listen and try to provide reasoned arguments in providing a response. In short I believe I at least try to respect people and treat them the way I desire to be treated myself and, in most encounters, I also see other Christians doing the same. That said, I think our answers can vary depending if we believe their is indeed any genuine interest in discerning the truths of the Gospel or whether someone is just throwing rocks. Jesus did the same thing when He walked the earth. He didn't always answer questions. He certainly didn't answer Herod's questions or Pilate's questions very much because he knew they really were not interested in spiritual truths or the Kingdom of God. The only time He did answer Pilate was when he was personally sincere. Then Christ provided the Gospel to which Pilate only replied, 'What is Truth? Jesus did the same with others who were caught up in their unbelief and were insincere, knowing their designs were for their own self promotion.
(4) Is there really anything that Christians and atheists can discuss about religion? Most atheists know all about Christianity already. Most Christians know all about atheism already. Christians can preach the same things that the atheists have heard and rejected. Atheists can ask Christians for convincing evidence that Christians can't supply.
I would take issue with your statement above:
- "Most atheists know all about Christianity already"
My experience and feedback, having had many discussion with atheists, is they usually have alot of head knowledge from books written against the Bible and Christianity but little understanding of the Bible itself. It's apparent most have never really read it but espouse things from 2nd or 3rd hand sources and web sites that conform to their narrative. Most importantly they know nothing about Christianity because it is quite impossible to know anything about Christianity without knowing Christ Himself.
In the harvest field I have found their is a difference from someone seeking to discern spiritual truths and those closed off to reason by the external forces of unbelief. I have found that this appears to be true whether those external forces are religious traditions or just that they are steeped in anti-religious sentiment. Most people like to think they are objective but the truth is we all have biases. There was a point in my life as well when I believed Christian testimony held no worthwhile value to me. I was wrong. Presently, like all true Christians, knowing Christ is everything. Denying His reality in my life would be akin to denying I exist. Unless I was willing to be moved by what God was showing me I would never have had that life changing experience that I desire others to have as well. What motivates me towards that end is God's love for me and for all peoples of the earth. Love then is the prime mover not intellectual discourse, which is useful in reasoning things out but falls short in being able to transform us. It is and alway has been love that transforms a person and I am living testimony that there is no love like God's love. Now science says nothing about love. It is not a visible force but it has changed history and changed the hearts of many lives. Some might say it doesn't exist but I believe they would be in a very small minority indeed. I see the arguments that God does not exist in pretty much the ame manner as people who do not believe in love.
(5) Does anybody know of a forum where Christians and atheists lie down together like sheep and lions to have fruitful discussions?
Hopefully we just had one 
Through all that life can throw our way, the love of God lights my way and satisfies my soul. I don't think atheism can do that and that probably paints my communicative perspective. Hopefully that is not problematic for discourse between atheists and Christians.
In Christ, John 17:20
