By providing everyone with free search to locate information, providing them with free high quality email, adwords to market their wares/services, adsense to monetize their traffic.
I thought there was the implication that google did something specific.
Google helps society. They provide good search. What separates then from Bing is that they operate with the idea of "do no evil". Bing are seen as copying (an idea - stealing) which is bad in society.
Zynga provides cheap entertainment, but that's not good for society. TV isn't seen as good for society anymore - it's passive. There's an opportunity cost to being entertained - you could be productive - learning on Wikipedia.