I have a lot of respect for Tim Berners-Lee, but he's basically incorrect about this. The problem with social networks is not a technology problem, it is fundamental to what social networks are. We don't call Stack Overflow a social network, because it's got a purpose, even though it has a lot of the same features as facebook. The problem with social networks isn't the software, it's that they aren't for a particular purpose, because if they did most people wouldn't go there (as most people don't go to Stack Overflow, because most people aren't programmers). If you want to make a social network with a billion users, you have to make it general purpose, and that means you do not have a narrow enough focus to keep the conversation on task (because there is no task). This means the conversation falls back to tribal bickering and shouting, because there is no focus/task to keep it from doing so. They're "social", with everything that makes socializing (facial expressions, tone of voice, only so many people able to talk at once) removed. You're not going to fix that with technology, because the thing that needs "fixing" is fundamental to what they are.
The problem with social networks, is that they're social.
The problem with social networks, is that they're social.