.
Lots of things, but some off the top of my head:
Communication technologies probably top the list. Sure, the Internet has given birth to lots of great communities, like the one where I'm typing this comment. But it has also created a hugely polarized environment. (See the picture on page 4 of this study.) It's ever easier to follow your biases and only read the opinions of people who agree with you, and to think that anyone who disagrees is stupid or evil or both. On one hand, it's great that people can withdraw to their own subcultures where they feel comf...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
If continuing the discussion becomes impractical, that means you win at open threads; a celebratory top-level post on the topic is traditional.