This particular bit of wank was in response to an interview given by Amanda Abbington in which she articulated a less than positive reaction towards seeing explicit fanworks of Sherlock and John (or Ben and Martin as she put it). She referenced concern about her children coming across this, I believe. Fan response was hostile and hurt and of course some of them started tweeting their feelings and anger at AA directly on her Twitter. She said she stood by her words. And thus this got even bigger. She has since apologized for saying things that hurt fans-

But I think it is also a firestorm due to many factors that came before. There are many fans of the show who are sensitive to the issue of queerbaiting or queer erasure. This first blew up big on Twitter when spoilers from the filming of TSOT came out last April. Abbington was also involved in that because there were folks who tweeted hate and death threats at her and/or about her character. A segment of fandom has been annoyed or sensitive to what they perceive as queerbaiting in the show from the outset and there is a lot of mistrust directed towards the creators and writers, especially Moffat in this regard already. And on top of this, many folks who knew Mary was coming did not think she would be staying and coming between their ship/shooting their favorite character/acting in a way they cannot get behind. And added to this are incidents in media and press events that have been perceived by slashers and fans of Johnlock in particular as mockery of them and their reading of the text (e.g. the Caitlin Moran fanfic reading event at the BFI in December, the portrayal of a fangirl in TEH and other things said in interviews).

So long story short, from where I'm standing, yes the continued existence of Mary. But this is only part of a much larger and complex picture.