Having seen some atrocious perspectives and opinions and Hacker News, being able to challenge some one or offer a rebuttal that doesn't turn into a comment storm is important. I don't want to engage with a troll. I want to give them a down vote and hope they're flagged and removed more often than not (I can't down vote anyone yet...).
But, there's a fine line between down voting some one because they're offensive, obtuse or obnoxious and disagreeing with some one's opinion.
I don't agree with you. In fact I outright disagree with your opinion on HN becoming an echo chamber. I believe HN is far an echo chamber, I also think it's far more diverse than most. But naturally and organically the opinions here tend to confirm with a certain bias and I like to think that's because we here on HN take more time to discuss our conversations and perspectives than the echo chambers you find on Reddit or on Facebook.
I want to believe HN is more in line with a common good, a common ideal and common truth of humanity (you can call me out on being naive here if you wish, I'm feeling more optimistic today than I normally do and I don't know why but let's let sleeping dogs lie, my cynicism is usually relentless...).
So, yeah. I disagree with you. But I wouldn't down vote you. Even if I could.
Edit: poor choice of words, sentence structure, I rushed it all to get it out in time in the hope one day I can get to 500 karma and down vote trolls.