For me it's a variety of things, but what originally brought me here was this. I'm about to be a bit long-winded; ready?
About eight years ago a Christian friend of mine, who tended to go to a lot of help forums, invited me to one he was in going through a stage of visiting. It was a small Christian forum called The Narrow Road. I looked around on it and answered a few posts.
Now, TNR was/is for teens who have problems they want to talk about, and although it was originally run by... someone, I'm not sure whom, the mods had generally gone away, with just a couple of them visiting once in a blue moon. This meant that whatever problem one teen posed (my life feels awful and I just want to commit suicide; why shouldn't I take drugs; my brother abuses me; etc.) the answer was pretty much always the same: pray/read a bit of the Bible, have stronger faith. For the suicide posts the response seemed always to be a slightly panicked, 'don't give up! You've got so much to live for!' or the occasional 'if you commit suicide you're committing the worst sin possible'.
Now, given that I have been an atheist for a long time so I've never looked to the Bible for solutions to my life problems (except for a few weeks/months, but that's another story), other solutions occurred to me with a lot of these problems. So I answered.
I am getting to the point, I promise. Bear with me!
I went back a couple of days later to see what had been posted since then. A few members had posted to say to me, 'you can't say that!' but a few had posted to say, 'Oh! Now, that's a really good idea!' So I posted a few more replies, and it all snowballed from there.
TNR continues to be as Christian a forum as it can be, but as it stands the owners have long-since deserted and I'm by far the oldest regular member there, so because I've been through a lot of the 'teen problems' a few times over, I'm pretty well-versed in practical solutions. We get a slow, constant through-traffic of new members, over half of whom are Christian if the content of their posts is anything to go by, plus a few who are angrily antitheistic. A few of the regular members are Christians and some simply don't seem to have said either way. The siite itself has a range of Christian articles.
So it's a strange situation but the end result is there's an atheist essentially in charge of a Christian forum. My position on this, these days, is: I'm not saying you shouldn't be Christian if that's what you want. But I refuse to believe - and will challenge - that faith is the only way to solve a problem. Pray if you wish to, but while you're going through a regime of prayer you may also want to try this other solution. And, once a new member recognises that's the way we do it over there, many settle down very nicely.
I don't want to argue against a person being Christian, I just feel passionately that a person should have a broad repertoire of responses they can have to a given problem. I believe that the wider your possible range of responses, the stronger, happier and safer person you will be.
TNR's only little and it goes through stages of not having any new posts, so when I feel like doing my agony aunt bit and there isn't anything to add to on there, I go to other forums, this one included. Occasionally I get reported for responding to a Christians-only thread, but if I see a problem mentioned where I think, 'it just needs an extra bit of information, or an observation to be made', then I'll do it. This forum is pretty good at being accepting that way. I've certainly encountered more puritanical forums.
Phew! And that's my reasoning.