Along these lines, CGP Grey's video about Anger Thought Germs is an excellent breakdown of why anger spreads like nothing else:

https://www.youtube.com/watch?v=rE3j_RHkqJc

You combine that behavior with social media, especially Twitter, and the symbiotic relationship with the news media. It's a non-stop anger generation machine. Rapidly iterating on these thoughts, packaging and surfacing the most potent, viral version. Any nuance and context long ago removed.