John suddenly gets very into a cause that is completely random for him. At least it seems that way to those around him, turns out back in college/post college/grad school he somehow got involved (I'm kinda thinking like Pride 2014 here) . He hasn't been overly active recently because he wasn't really needed and than Sherlock happened but he's being asked to help and he will .

+John being very passionate and his temper showing.
++He asks Mycroft for help.
+++People thinking it's a mid life crisis