I've been banned from Christian forums (well, from one) and I can assure you I never arrived with the express purpose of breaking the rules. If someone is going around deliberately breaking rules then maybe it is their desire to be banned, but then why show up at all? No, I think many atheists are inadvertently breaking the rules.
I don't think it's inadvertent at all. I think in a lot of cases it's a deliberate act of rebellion against Christian authority, becuase they hate Christian athority the same as the hate God's authority in the Bible. Some cases I think they do it just to see how much they can get away with.
I might be way off base with all of this, but that's the impression many atheists leave on me.
I can tell you that I am very cautious about how I post because it is so easy to slip across that invisible line, and yes I think the line is often invisible. I can't tell you the number of times in the past that I've been accused of insulting God or the Faith when it was never my intention to rouse that kind of ire. I am more aware of it now because of the number of years I've been at this, but when I started out I crossed the line many times. Often I was left dumbfounded by the reaction that I sometimes received, and I believe the raw nerve I was cutting into is frequently more exposed in some people that it is in others.
Yeah, I bet you were left dumbfounded, same with many other atheists who get banned. They can't figure out why, so they play the victim card of "boo hoo hoo, look at me, they banned me, poor me," or they'll play a superiority card like "they banned me because I was right," or some combination of the two. However, it's often that neither is the case. They play those cards because they are blind (a lot of times willingly) to their own pride and arrogance. It sounds like this used to be the case with you, and over time you learned how to respectfully conduct yourself towards Christians. And when I say respectfully conduct yourself, I'm not talking about how you respectful you conduct yourself in your own eyes, but rather you recognize how Christian authorities view what's respectful conduct.
Based on what I said above about rebelling against Christian athority, this is why my picture of the typcial atheist is a spoiled 5-year old screaming and crying when he doesn't get his way. It all has to do with issues of how they handle the authority over them and discipline. (yeah, there's not much in terms of discipline on an internet forum other than banning, which is really just a slap on the wrist in terms of overall consequences, but some people obviously can't even handle the slightest bit of discipline well.)