I think you're on to something - many commenters (myself included) probably vote based more on agreement or disagreement than on anything else, and this necessarily reinforces the groupthink. If we wanted to fix it, the way to go would be to define standard rules for upvoting and downvoting which reduced the impact of opinion. It cannot be eliminated - if someone says something stupid, for example, saying it should not be rewarded - but a set of clear guidelines could change the karma meter from a popularity score to a filter sorting out the material worth paying attention to.

I think a well-thought-out proposal of such a method could make a reasonable top-level post.