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.
edit: assuming you're not being sarcastic, can't tell.