a button to flag for review is one thing, but hiding content purely based on public user input is generally not so great. imho, HN has a great system of only allowing high-karma accounts to access the power of the downvote. it's a similar idea to selecting community moderators to go over any content flagged for review, but just a little more automated.
It will always be possible to search without preference filters, because there's an economic incentive to providing all-inclusive indexing decoupled from the ratings system. However, being able to express only approval inevitably leads to a crowding-out problem; witness the ever-expanding ration of ad to content and the plethora of competing buttons to like/+1/tweet/digg/zzzz.
Lately I find myself filtering more and more; after blocking disqus, for example, I can't see comments on most news stories any more and this has been a signal improvement. I was a big booster for the democratization of the communication commons back in the 1990s, demanding that every media outlet put public comment facilities on its websites so that everyone could have their say on news stories and so forth. Boy, did I get that one wrong.