As a coach I have seen my fair share of impulsive posting to different social media sites. About five years ago I almost had an entire track season derailed by some parents posting on social media because their children weren't competing in events they thought they should. It bothered me and I confronted the parents. I wanted to set up a meeting and discuss things and the parents refused. Everything got patched up and the season went on, but even years later it still doesn't feel good.
Social media is an awful "out" for parents. We have had major issues this year with parents posting their opinions on different sites. It looks so bad for people who are involved! It is horrible that many coaches/teachers do not get to defend their sides of the situtation.