Most people won't even let themselves imagine what could be done with Google if evil was an option. How many hours would it take to compile a list of everyone who searches for incest porn and correlate that with 'people who are judges'. Considering that the incest fetish runs as high as 10% such information could be used to perform a bloodless coup. Call the legal system nullified, and lobbyists obsolete.
And that is just one facet of the simplest way Google could be used for evil (blackmail). There are infinite ways Google's information asymmetry could be exploited, and most of them would be completely invisible and 100% effective.
Thats why I'm glad we have Sergey and Larry running under the banner of "Don't be Evil." It shows that even from the beginning they realized they were going to wield terrible power, and they were a bit honest with that fact.