Exercising their free will to sacrifice that free will, perhaps? Ha!
Grasscarp: firstly, it depends on the atheists in question. I don't think that answerbank is necessarily representative: the majority of atheists probably keep their mouths shut, or at least only talk about it when prompted by friends or theists who bring the topic up in the first place. On the other side of the coin, how many people out on the street (a) preach and proselytise about their (usually Christian) faith in loud tones, condemning passers-by as sinners or at least speaking loudly, and (b) how many of these street-preachers have you heard talking about "there is no god, and actually I don't have much more than that to say really"? Perhaps the street preachers aren't representative of the religious either. On the other hand, Matthew 28:18 suggests that it's the job of Christians to talk about their faith to the wider community. In which case, you shouldn't be too surprised when atheists feel obliged to respond -- and perhaps even to start the conversation themselves.
Not only that, but at least some of us would like to discuss the topic because we might want to understand what motivates people to have a belief, or to ignore/ overlook/ reject arguments that persuaded us to adopt a position of non-belief (or disbelief).
Speaking now for myself here, I've also spent most of my time as an atheist wondering what it means for my theistic (most Christian) friends. At best it means that on this topic at least I disagree with them. At worst, given the apparent ease with which most arguments in favour of religious faith can be rejected, that presumably implies that they are irrational or worse. I'm still not entirely comfortable with that, and so I'm probably spending more time than I would otherwise in the R&S board in part because I'm still secretly hoping that I might be wrong after all. So it would be nice to hear what theists have to say in answer to questions.
Unfortunately, most theists on AB seem to fall into two camps: the smaller those who don't engage in a meaningful debate because they've already made up their mind and dismiss out-of-hand both the points atheists make and the people who make them. The other camp seems to be filled with people who don't really want to talk about it, and pointedly say so, and ask us to stop talking about it. (There's also presumably a third group, those people who are religious but never even mention it or engage in the debate whatsoever.)
At any rate, it would be nice if theists started to spend less time complaining about having more time to talk about why they believe and more time actually talking about it, and responding to arguments and counter-arguments.