Wikipedia summary
For those who don't have the time, here is a very basic summary.
All humans attempt to escape from death by immersing themselves in culture, which acts as an escape by providing symbols and ideas that provide their meaning of life (religion, philosophy, nationalism, etc).
When confronted with the idea of their own death, people are more likely to stick to and support their culture/ideas and become hostile towards those who threaten their world view.
Example
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In an experiment, people were asked to fill out a questionnaire on their personality and participate in a food experiment. Some questionnaires had questions that would remind the people of their death. In the food experiment right after, people were asked to use their judgement to give a person who was of a vastly different culture from them a certain amount of incredibly spicy hot sauce by pouring it into a bowl. Hotsauce has been documented as used with an intent to harm. Those who were reminded of their death used twice as much sauce on average than those who were not.
As a result, the authors conclude that a lot of human aggression is a fear of their own mortality, known as terror management theory.
Could this phenomena be the result of so much debate online? We are reminded of death constantly, even if we are unaware+ Show Spoiler +
(an experiment similar to the hot sauce experiment was done except by flashing the words death and another word that has the same frequency and length in the English language across a screen while subjects were doing a simple online task. The words flashed so quickly not a single patient was able to recall what the word was reliably when asked later. Despite this, those who were flashed death displayed the aggressive attitude, supporting the theory and subliminal cognition)
In a game such as starcraft, ragers could simply be angry due to the fact that their approach towards the game, or in other words their mentality (perhaps playing macro or a sense of fair play) is threatened by someone of a different ideology (cheesing, doing anything to win). It may explain why there are so many people online that BM when they perceive something not going their way. It may sound like a stretch, but a war game such as starcraft reminds us of our deaths, so we hold closer to our ideologies. When something threatens our ideologies (such as losing, which threatens our idea of how to approach the game), we become angry and rage.
Although this theory does have its problems, I just thought the extent to which the reaction could be evoked was interesting and wondered if rage online is because of the online games.