It’s hard to answer a question like this, often because of the binary expectation that if a thing does harm then it cannot possibly also do good, and vice versa. The good that social media does comes from the unprecedented rate at which it brings people together, without regard to distance or time. Unfortunately, so does the harm it causes.
The internet’s scope also erases human intuitions about the scope of actions we take there. In a room or on a street, we have an idea of how far our voices carry, but a single tweet can fly around the world before its author steps off her plane, as happened to Justine Sacco.
