It's important to highlight that Christianity StackExchange has a very different atmosphere to Mi Yodeya. Christianity SE is very much true to its mission of being a Q&A site about Christianity. It is not a Christian site. And that post on meta isn't just a claim. It's lived up to throughout the site. In fact, it was recently brought up again in discussion of the design theme.
Just a heads up, we aren't a church and don't want to look/feel like one. In fact I think some visual clues that this is a secular QnA site with topic/theme of Christianity would be welcome.
I'm saying the idea is that we are not a Christian site. We're on the outside looking in, not on the inside trying to reach out like church and "Christian" sites do.
Bearing that in mind, asking a question about Christianity, or indeed answering a question on the subject of Christianity should probably not necessarily be seen to count as aiding Christianity in any way.
Analysis of Jewish legal reasoning in this situation I will leave to others, I just wanted to clarify what the situation actually is.