What else can a filter be aside from a bias? Clearly, I'd want a search engine that's biased against spam and generally against "automatically generated" content.

It's hard for people to wrap their heads around how many search judgements are inherently editorial decisions - and how much of this is OK. One factor is that mainstream American news, from Hearst to the NY Times spent a long indoctrinating people on the claim that their position in the political spectrum was "balanced" where everything else was "extreme".

One actually useful thing a search engine could do is allow it's users to see it's biases and even configure their particular preferred filters - within reason. Could be a selling point.