Because we all know the old joke about arguing on the internet.
And in addition to that many of us have seen what religious arguments on the internet did to reddit.
The story itself may be a perfectly fine, but I encourage everyone to keep HN a religious debate free zone.
The problem is not religious arguments - the problem is ranting and not reasoned debates (recently Reddit's Palestinian / Atheism / GOP bashing / Obama posts became intolerable).
This discussion seems civil and well thought out. A good example is dominik's post above – it is pretty well reasoned and factual post and is non-inflammatory it is a good post (even though I am not Catholic).
It is not the nature of the argument that destroyed Reddit it is the way in which it was done. And this can happen with any topic not just Religion.
Reddit religion is sickening. As an avowed atheist I can't stand to read the atheism subreddit - it's far one shallow and one-sided than any similar religious bigotry, and that's really, really hard to achieve.
I'm really glad to be reading the debate here. Both sides are being calm and reasonable, which I love. It's proof that the Internet can be civil.