I don't see that really...look back at the thereads...it's all still there..there was a lot of enthusiam and excitement when we learnt Mary would be in 03 and AA would play her.
When TEH aired more Mary threads started , @most people loved her , but the -something about Mary -thread appeared and suspicions were aired , which grew during TSOT and obviously proved true in HLV.
Thats when dislike of Mary started..in a perfectly normal way..Mary was a professional assasin..had lied to and decieved John..and shot Sherlock..no one needs a 'need' to be appalled by that.
Whats wierd is the fanatical defence of Mary and crapola and inventive excuses to turn a highly trained liar and killer back into a fluffy bunny.
I think a lot of it ( irrational need to defend AA and Mary ) sprang from early sensationalised media rubbish about AA getting death threats from crazy fans..nonsense I found very hard to believe anyone ever took seriously.

It seemed to me Sherlock wanted to arrive just after Magnussen left and while Janine was still there to let him in and Mary delayed Magnussen.
Not really complicated.
To add a complex back story to HLV after what will be a three year hiatus. ?
The writers don't and won't do that...we have to go by what we saw in S03..creating imaginary back stories and scenarios for Mary in HLV would require a lot of back tracking on a decision the writers already made.

I know for modern clinical diagnosis and etc in real practice , terms such as sociopath and psycopath are no longer relevant , however for laymen and general audiences and particularly Moffat , they are.
The writers seem quite fascinated with the subject and use them a lot in their works and interviews, and they are laymen writing for laymen...I suppose.
So for Sherlock and a lot of modern fictions , the old fashioned but popular psycopath and sociopathic stereotypes and persona's are still very relevant and fascinating. 
Sureley what AA meant with what she said was obvious, and she wasn't hinting Mary needed an ASBO , but more that Mary had something of Norman Bates ( or a typical psyco killer ) to her character. 
It could of course been a joke , but her further tweet apologising if people were upset but that we all knew it anyway , seemed to confirm the psycopath opinion.

If not in the SP then in S04..they will cover Sussex vampire..perhaps making reference to the theories back in the twenties and thirties etc that Holmes was Van Helsing in disguise.
Obviously this will give rise to speculation on not just Doyle and Wildes aquaintace but.. Doyle ,Wilde and Stokers decades of friendship...the homoeroticism in Dracula..and othrr interesting things.X

Informative article here...

https://muse.jhu.edu/journals/elh/summary/v061/61.2schaffer.html

and inspired by reading something welovethebeeker.tumblr.com wrote on silhouettes in SH and Dracula/Nosferatu

http://welovethebeekeeper.tumblr.com/post/127316440073/the-silhouette-some-pastiche-and-looking-for

Does anyone think it's likely that Mary and/or Magnussen knew Sherlock was alive all along ?

I agree that theres a lot of wibbly wobbly writing with the bonfire thing.
I think Cam had been in contact with Mary before the wedding though , it looked like she recognised his name and seemed worried not surprised when Sherlock read the telegram.
It kind of makes sense to me that Mary knew of Cams bonfire plot, (that according to cam didn't endanger John at all) , because thats likely what made Mary decide to kill Cam.
Maybe she had been or was willing to go along with Cams blackmail until he used John?

Admittedly it would be easy to kill Sherlock in hospital   , but how on earth would she get away with it?Surely she didn't manage to get in and out of such a busy and highly observed place without being seen or caught on camera, not to mention that again John also would be a suspect and likely close by. I don't think anyone has suggested Mary had any intention of attempting to kill Sherlock there anyway.
The contention was Mary shot Sherlock to prevent him telling John about her double life etc.But that is not even mentioned until after Sherlock survives.Sherlock says her problem was 'the witness' to her crime.
Indicating she shot Sherlock to cover the crime and escape the scene..... if Mary thought Sherlock knew it was-not tell John- the hospital threat visit would not have been necessary at all.?
Actually in many ways the hospital threat isn't needed at all .Sherlock doesn't need to be told..don't tell my husband I shot you or that I was going to kill Magnussen...thats kinda lol isnt it?
Which makes the whole scene superfluous anyway.
So why did they include it.

Swanpride wrote:

Yeah, but Mary's intent wasn't to kill, it was to delay Sherlock long enough that she could talk to him later on. And if she intended to kill Magnussen...well, if she had done it, Sherlock wouldn't be forced to do it.

 
Not sure about this .The reason Sherlock gave was that Mary shot him because he was a witness to her attempt to kill Magnussen,  not to stop him telling John , but had a moment of sentimentality and so didn't take the immediate kill shot.Thats where 'shortsighted' came in , because once she realises Sherlock has survived it becomes obvious he will tell John, thus she threatens him and goes prepared to silence him permanently at Lauriston Gardens.
Having her shoot because she expects Sherlock to never tell makes her stupid and we know how smart she is.
Shortsighted...is a bit better...I think.
Either way it annoys me that they make her yet another woman who when faced with Sherlock throws all her training and smarts out the window and gets caught or beaten because of sentimentality. This is another reason I would prefer Mary had a reason -other than sentiment-to let Sherlock live.
But eh Moffat and women....

Yes . I get the impression from everyone involved in Sherlock that ultimately everything is supposed to be funny banter.These people are comedy writers and humour is the backbone even when they do drama and angst.
Mary being so much of a 'blank page' is deliberate , if they gave us reasons to sympathise or empathise with her , it breaks the humour .
I think some of the discussions and recent posts about S03 and Mary have become a bit Jerry Springer audience ,which is fantastically hilarious , and likely the writers intention. So nice to see a return of the witty satirist.

Additional Edit.
Apologies if OT or thread drift.Seems to be a lot of crossover discussions and its become difficult to keep things straight .

Like a parody of a parody...very lol.Not sure what to make of it but I know who to blame it on :-)
John ! is brilliant.