This person gets agitated and outraged, so as to get attention as a moral torchbearer for an issue. Often they forget the issue and move on to next issue with out making any effort to support or resolve the issue with in few hours.
I think you’re looking for demagogue:
a person, especially an orator or political leader, who gains power and popularity by arousing the emotions, passions, and prejudices of the people.
Folks who push social ideas via outrage are said to be practicing demagoguery, which is totally a word I didn’t just make up right now to win at Scrabble.