This is a very broad topic and some smart person could probably do a doctoral thesis on this subject. The internet is an amazing technological gift and I don't think anyone envisioned the sort of potential it had when in its fledgling state. The ability to connect people from all over the world in real-time has unlocked an unprecedented global community.
It's facilitated the Arab Spring, which the jury is still out on whether that is going to turn out to be a good thing or a bad thing. We've seen a young woman (Justine Sacco) vilified for making an off-color tweet in a poor attempt at humor that cost her job and ruined her reputation. We've seen young people commit suicide because of cyber-bullying. Harassment and death threats are rampant. And what is turning into a horrible custom--people jumping on the bandwagon of something they have very little knowledge of and creating a mob mentality. All of these things have happened and are happening, and it's sickening. Gamergate, Puppygate, leftwing vs. rightwing politics, I don't even want to get started on the details, but these things impinge on my daily visit to the web. News spreads at a viral pace now and people don't bother to take the time to see if things are true or not, they just take at gospel because everyone else says it's horrible. It must be bad if so many people say it is. It's as if a "journalist" from a gossip magazine is running the internet.
Why is it we want to believe the worst in everyone? The corporate world is not immune either (Examples of Social Media Crisis.)
And here is the worst part. If you speak out against something you are inviting the hordes to your doorstep. In some cases, literally. I'm hesitant to take a stand on any issue now. Who needs that kind of drama in their life? I know I don't, but I do think about stuff, and want to take a stand on things I feel strongly about without being singled out as the target du jour. Free speech should mean we all get to have a say, and be able to do it in a civil manner.