This argument came up on reddit. I think the reason this happens is that there's a certain mindset that says that absolute truth is extremely simple, and that deviance from that truth is a black-and-white affair. On Hacker News, we see mostly the atheist side of this black-and-white spectrum: the sort that denies religion any benefit, and which denounces people who disagree as insidious and festering.

That mindset appeals to programmers, in part because it's a very lazy mindset that allows you to quickly judge complex things and focus on the very specific thing that you care to focus on. It's the same mindset that encourages blind libertarianism. The problem with it is that it discourages intellectual discussion and leads to flame wars. That's what brought reddit down: a mass of people who were willing to instantly denounce people, and who led to a very hive-mind situation.