Like MS and Ubuntu, they purport to protect us from ourselves. They present themselves as a public service, but, in truth, they are nothing more than a particularly virulent form of vigilantism. When I was first exposed to WOT, I went searching the site. Nowhere could I find a means to redress an incorrect judgement. Perhaps that has changed, but it forever branded WOT in my mind as authoritarian and dictatorial. At least K9 does provide a readily accessible means to protest their judgments, but that does not make them any the less vigilantes. All such sites arrogate to themselves an authority they have not earned and do not deserve. They assume the right to stand in loco parentis for all the Web.
Even some of the anti-malware sites carry their reviews a bridge too far, and display similar obstacles to protest/adjustment. My personal feeling - and I know many who feel the same way - is that if I get hurt browsing the Web, on my own head be it ... I neither need nor want some Orwellian group dictating my activities.