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I do have a lot of feelings on John's immediate reaction (commonly known as Rhino Noises) after Mary dies and while it is a questionable acting choice on Martin's part, I see the sense in it and here's why. It is clear from the very first moment that John is on screen in ASiP -
that he is dealing with a lot. PTSD from the military, it's implied he doesn't have a good relationship with his family, and he lives for adrenaline. He finally meets Sherlock Holmes who gave him a whole new life so different from the one he lived and then all the sudden -
that is taken away from him. For two years. You add what you think is the death of your best friend on top of everything else he's already dealt with and it's a lot - then Sherlock comes back and all the sudden things have changed because Mary's here and John's almost moved on -
So, John is dealing with the shock of having his best friend someone he loves with all his heart, walk back into his life and knowing things will never be like they were no matter how much they both wanted them to be. So John has endured trauma, grief and now shock.
It's implied and shown that he has a few tenancies such as controlling his anger and the authors mentioned something with alcohol representation in the series as well, so he has a few habits on top of that too.
Then Mary is revealed to be an assassin -
Then Mary is revealed to be an assassin -
Which clearly pisses John off, and I think he only really stayed because she was pregnant and he knew as a parent it was probably the right thing to do, not for Mary but for his child. Given the option I think he would have gone back to Sherlock.
Mary's revelation and her manipulation of both John and Sherlock in some parts adds to the growing pile of things that John has endured. But it's obvious he still loves her. He wants to be part of her life because he is loyal to a fault (or so we thought).
But, when you lose someone you love, regardless of the relationship you had with them, there's always going to be some sort of grief. It might not last for long or come out in the way one might expect but we all grieve in our own ways.
So John has endured war, PTSD, marrying someone who turned out to be nothing like who they said they were and despite that he still loved Mary, and had a child with her and now that child doesn't have a mother and he is a single father (though Sherlock helps with Rosie later)
And so in that moment, when Mary finally gives out, all of John's world comes crashing down, I think a lot of this was the final straw for him. It wasn't right for him to have blamed Sherlock, but oftentimes when we're in a position like that it's easier than the other options.
You can't comprehend what has just happened so it is easier just to find something or someone to blame, and in that moment, for John, it was Sherlock. I don't agree with all of his actions throughout season 4 but I understand them in a way.
John resorted to anger -- to rage -- when this happened, because he feels like he has no one. He's a single parent, he feels like his best friend has betrayed him and no one can truly understand everything that he has gone through -- or so he thinks.
So when that realization comes crashing down on him, all of this grief and pain that he has endured -- that John knows he doesn't really deserve -- it's an ugly feeling. It's sad, it's angry, it's a monster, and so I understand why the first noise he made was a growl.
Because he feels like he can't ever win a chance at happiness, that something always intervenes. When that moment hits you, it hits you hard, and sometimes you just can't do anything except let out a nasty, monstrous scream. I will defend S4 John until I go to my grave.
