I don't think that is true, what will happen is people browsing hackernews from work (in not particularly liberal work places) will not be able to read posts. Even if people choose to (incorrectly) use the .xxx extension I don't think it's going to push people to stop assuming .xxx is pornographic.
edit: assuming you're not being sarcastic, can't tell.
It reminds me of bands who have offensive names, or developers who name their software after offense words.
They might not care about "rules" or "society" or this and that they might say, but it's inconvenient for me. Even though I am not offended easily, some of my coworkers, bosses, classmates, people on the bus, etc might be. If it's inconvenient for me to view the site, use the software, or have the album art showing on my iPod/computer, I'm going to avoid it even if I like it.
That's their choice, I understand. They made the determination that there are people who could appreciate their work but aren't willing to take the same hit to their reputation. It just disappoints me as a fan.
It was automatically blocked by my work filter as porn. First time I've even noticed a .xxx extension, and I didn't notice it until I noticed it was blocked.
Yup, still hesitant to click .xxx links at work even if it's not filtered. Didn't see any repercussions after the last time I accidentally clicked one at work (another HN article)... though I didn't get promoted this time around... correlation? I'm going to make myself feel better and say yes.
edit: assuming you're not being sarcastic, can't tell.