Traditionally, newspapers had that same conflict, where political groups of all stripes can buy some of the most visible space to advance their causes, regardless of truthiness. In fact, you could even buy an ad in the NYT to slam the NYT itself: http://m.deadline.com/2013/05/scott-rudin-slams-nyt-reporter...

Think of it this way: this kind of ad purchasing allows for the editorial side, or in Google's case, the search results, to remain independent of outside influence