Here is an interesting article I found that may shed light on Sherlock and John being able to forgive Mary's deception and shooting in HLV  http://io9.com/why-we-hold-grudges-about-little-injuries-but-forgive-b-1538315074  . Of course there are many other factors involved plot-wise, and being fiction, many liberties are taken, but it is nice to know Moftiss isn't entirely off the deep end.

I'm aware that there have been many discussions already on the forum, so feel free to move this to the appropriate thread