The alternative to confirmation bias bubbles is, especially for social media, showing people stuff they might not like or agree with--the problem is that this isn't great for business, and generally get's people up in arms.

A great, very recent, example of this was reddit making /r/TwoXChromosomes, a subreddit dedicated to women's issues, a default sub (meaning everyone, even non-users, are automatically subscribed). The stereotype demographic for reddit is young white males. I have no way of actually verifying these demographics--I'm not sure they do either.

Yesterday, a comic about the casual sexual harassment caused by men was posted[1] and although there was some valuable discussion, most of it was pretty awful to read (the further down you scroll, the worse it gets). Although we'd like to believe that engaging in debate / conversation / dialogue generally cause us to have empathy for and understand the other side, the opposite tends to happen, especially in large, anonymous communities. And this is in a venue where the quality of participation IS (supposedly) based on the value of the discussion.

Although I think you're right that most websites (Hacker News included) suffer from only having up and / or down votes. It's possible that a more complex system might be more useful. Maybe in addition to the like / dislike paradigm, it might be useful to add quality / not quality functionality.

[1] http://www.reddit.com/r/TwoXChromosomes/comments/2d85wt/next...