Mycroft Holmes was going to kill his brother.
How on earth had Sherlock managed to get himself in this position? It was in that moment Mycroft found himself wishing that his lunatic of a relation really was a sociopath. Because if Sherlock didn't care so damn much, he wouldn't be where he was now. He wouldn't be in the line of fire, he wouldn't be going after a real (and very powerful) sociopath, and he most certainly wouldn't have had a gun pointed at the head of one of the most dangerous men in the world. And most importantly Mycroft wouldn't have been terrified that he was going to see his brother die.
Well this was Sherlock he was talking about… And Sherlock wasn't Sherlock without the constant threat of mortal danger.
No, it wasn't Sherlock that needed to be emotionless, it was Mycroft. Mycroft needed to be able to process and deal with the situation before him without flinching, with the unwavering certainty that befit a man of his standing, regardless of personal connection to the matter. He needed to be able to do this, but he couldn't. Because neither of the the Holmes brothers were sociopaths, as much as they both wished they were sometimes.
"DO NOT FIRE ON SHERLOCK HOLMES!" Mycroft cried out, uncaring that everyone could hear the clear desperation in his voice. Oh Sherlock what have you done?