I don't think Facebook and Twitter, specifically, are hurting society.
Do we have people who obsess over them, log in every day, post every hour, and so on? Yes. Of course we do. But for every one person that does that, you have one person who doesn't have an account, one person who uses it only rarely, and another person who only uses it to keep in touch with friends or family who use Facebook a lot.
There are many benefits to using Facebook, and that is the truth. When you describe the extremists, you forget that they are often only a small percentage of users, who get 95% of the publicity in anecdotes or the media. While technology provides an easy example of idiocy (Tweeting about seeing someone being held at gunpoint, for example), it would not be the technology hurting society - only those who use those technologies irresponsibly.