Personalization and polarity

In the more than 20 years I've been studying AI I've discovered that every decent knife has two edges. Even those knives that seem like really, really cool ideas when you first grok them. How could giving everyone a free editorial column be a bad thing? and how could improving access to all that new content not be beneficial?

Anyway, I can't resist responding to Fernando's response to Matt's response to my response to Lauren Weinstein's posting (are you following all this?) on search-term polarity.

The original post by Lauren Weinstein that triggered this thread was about the visible global impact of search rankings, but William's discussion suggests a less global but possibly more powerful effect in search personalization, of whether a personalization algorithm could become a strong reinforcer of prejudice without the counter-pressure of critical discussion of globally visible search ranking.

Here's an even broader suggestion: could just having more and better access to more and more diverse content have the same effect - i.e., is the growing blog world "a strong reinforcer of prejudice without the counter-pressure of critical discussion of globally visible" content? It's certainly easy enough to fill time reading political commentary that you can be 99% sure you'll agree with - and look how bitterly partisan the country has become, and how little is now universally accepted as correct.

Maybe Matt or Fernando know whether anyone's ever looked into whether the effect I'm speculating about is real - and if it is, what could we scientists do to create the appropriate "counter-pressure". Ideas, anyone?