I think people are pretty wrapped up in their emotional responses to the show and the characters. And there’s that whole extra element of non-reality and suspension of disbelief.
The real difficulty is that this show plays with those lines deliberately, and also by accident. We have characters who lie and are otherwise unreliable. It’s entirely possible and believable, for example, that Sherlock deliberately made up that “she wasn’t trying to kill me” thing simply in order to push John toward feeling sympathetic.
It’s equally possible and believable that the show is asking us to believe that that is the actual truth, and to handwave the whole RL fact that shooting someone in the abdomen is a situation that leads to a person not being able to guarantee that the target will come out alive, regardless of how good their aim is.
But the general point is that sometimes the characters lie, but then again sometimes it’s the show that’s saying “We’re not standing in real life here, just work with us on this” (like when we have all these British people running around with guns and not being arrested for it). And then sometimes again a thing happens even though we know reality doesn’t work that way, but it hasn’t been made clear to us that right now we’re not playing by real-life rules, so we don’t know whether it’s tv reality or the characters lying.
At that point, viewers have to figure it out for themselves. And sometimes ‘figuring it out’ involves coming up with their own headcanons and imbuing them with a bit of themselves to make it feel true enough not to feel like their favorite show’s left them flapping in the breeze.
And once you’ve done that, it can be pretty painful to have another fan yanking your chain. It tugs at the heart more than it might otherwise do.
All of which is to say, in the real world it’d be completely batfuck for somebody to be okay with a scenario like that. But one of the responsibilities of a well-told story is to delineate to the necessary extent where the boundaries of the fictional world vs the real world fall. And since Sherlock has done a crap job of that this season, many viewers are stuck in a sort of story limbo where it’s really hard for them to figure out, for the purposes of the story, what they’re meant to consider acceptable and ‘real.’ In that situation, fans don’t feel that they’re being asked to declare whether your spouse shooting your best friend is actually okay. They feel they’re being asked to declare whether the show is trying to say whether it’s okay.
And I think we can all agree on this one thing: this season, it has been really difficult to figure out what the show is actually trying to ask us to believe is happening.