As a reader, I find it's much easier to comment, disagree, debate, etc. online. Online, it's more about one person saying something, then another person commenting. It's hard to be interrupted (unless you're chatting in real time). This means that you have to (or get to) respond to what the person is saying/typing, not necessarily the person him or herself. 

I'm more likely to share what I really think online b/c I can take the time to write out what I want to say and make sure it's exactly what I mean. And even though I use my real name, with links to my real self, there's still a bit of a protective bubble with the Internet b/c it's not face-to-face. (I actually wrote a whole paper once for a comm theory class about online anonymity and how that makes it more likely that people will speak out about their true beliefs/thoughts - but I digress.)

Social media, like anything else online or in life, is as good as you make it or as bad as you make it. It's not fool-proof and sure, it's not perfect, but so few things in life are. Disregarding something (like social media) because of the <i>potential</i> for something bad also means you're missing the potential for something good. Sometimes you just have to have a little faith, take the leap and keep your eyes wide open.