I find the effects of social media very interesting.
Some say that it has caused people to become easily outraged.
But I think that it has also shown that virtually every human being has a nerve just waiting to be triggered by the right prompt.
Or...
Some of us choose to avoid it altogether, thereby also avoiding any possible stress thereby !!
Yes more and more people are discovering that approach!
Count me among those who avoid it... as long as Nth Circle doesn't count. 
IMO, the (anti-) social medias are sites like fecesbook, twatter & other very dynamically updating sites that are right in your face demanding constant attentions as well as offering multiplayer gaming, etc...
Yes, some forums have games and shoutboxes and some even do a bit of live updating - but fortunately (for me at least) such sites are easily avoided.
Underestimating the importance of stress management is a serious & costly error IMO, but at the same time, some folks are so addicted with bad/destructive habits that such thinking is totally off their maps.
(I get to see the above 'live' as I live with someone fitting this description & and who is also paying for this mistake, big time !!)
The reactions to her tweet are thought provoking. My take is that Lizzie was awkward and probably too humble to just have told the women that she swam in the Olympics, which may have made the woman feel awkward, and may have made Lizzie seem like she was boasting. It appears the love/hate/between reactions on twitter are a sign of our knee jerk reacting times. Perhaps we should think about something for a while before reacting. But is the problem social media or human nature? From time immemorial humans have been disliking one another and killing one another by the millions, not to mention loving one another. So one might argue that social media hasn't changed how we behave but just provided another venue for the exhibition of who we are.
It a good thing Joshua Bell didn't tweet about all the people who walked by while he was playing in the subway.
A agree with much of what you say.