It's not just Reddit.

One of the tragedies of the Internet is that it deprives people of the opportunity to see the faces of everyone in the room when someone's talking. In real life, you can see that two people are loudly arguing and the other eight people in the room are looking at each other uncomfortably, or wandering away and congregating in a different room. On the Internet, you're not even aware of anyone but the hotheads, so it's all too easy to forget that they exist, and come to believe that their opinions are normal.

Which, since nobody likes to feel like they're the only one who thinks a certain way, probably does end up discouraging people from having moderate opinions over the long run.