I have played a couple of months total, with pauses of years, I think in totall less than 1 year, mostly team games(mostly 2v2), i got to diamond in 1v1 and masters in 2v2. I have played probably some 10-20 thousands of games, mostly 2v2 games, should be something like at least 90% of the games were 2v2.
I think about 5% of 1v1 players and 10% of 2v2 players, which I have met online, clearly developed severe mental illness, and also without realizing it, and they cannot control it. This is a serious issue that should be addressed because it is dangerous and scary. I think the causes are scientific properties of brain and body during massive amount of gaming and the nature of massive gaming. The need to win(like gain mmr/achieve high rank/not lose), the cruel reality of either playing according to the rules of the game(design) or simply losing like a somebody clueless,.
It is dangerous! better not list all the reasons why.
I should warn you all about the possibilty of getting a full ban from blizzard themselves(ofcourse including battlenet and the game), and also from anyone at all - like for example websites and events, and I really dont want to add some more scary things(which really are beyond belief so watch out).
I will say just a little bit, only to explain a little. So, imagine, after 12 hours online, and with a tired brain, a person isn't fully aware of his condition, a little bit of arguement or disappointment from the game results can result in players being literally evil and even develop very harsh view of life as a sport-victory only world with winners and losers, or additional problems, some god help us distored mind which can actually be not in control of itslef and also not aware of its dangers by its host and more.
So i think gaming need mental health professionals to do some research and give some guidelines on how to stay mentally healthy and also save those who have gone mentally ill, and save those gone extremely mentally ill to the point they massively evil against others.
Edit: It think this is what caused some people, including big personalities to stay away from sc2 and not explain why.