Sherlock Holmes wrote:

.....We know he's comfortable with violence. EXAMPLES:

ASIP
He tortured the dying cabbie for information on Moriarty.

TBB
He beat up and knocked out the assailant in Baker Street during the beginning sequence
He fought with the Chinese gangsters at the circus show
He fought the gangsters at the end to rescue John.

TGG
He shoots the wall.
He fights the Golem.
He brandishes a gun at Moriarty.

ASIB
He fights with John.
He fights off assailants at Irene's place (vatican cameos).
He fires a gun in the air.
He beats up the American and throws him out of the window. (several times).

THOB
He fires a gun at the hound.

TRF
Lots of gun brandishing at various points
Moriarty knows that Sherlock is capable of torturing him for the information to call off the assassins, therefore he kills himself to force Sherlock into jumping.

I think if Sherlock was backed into a corner, then he would kill, if it was between the life of the assailant and his own life or John's, and there was no other way round it. I can't actually imagine this happening though, because you normally always have a choice - you can choose to shoot them in the shoulder or leg or something non-fatal, and I think Sherlock would go for that option. Not because he is afraid to kill, but because he enjoys bringing people to justice and seeing them go to prison etc. Thinking back to the Golem, Sherlock fired at him A LOT, and quite indiscriminately too, then was extremely angry that he got away. I don't think he was planning to kill him though. Just shoot him, injure him, then interrogate him.

There are no incidents in the canon of Holmes killing anyone so I don't think Moftiss will ever go down that road, although I think we must believe that Sherlock COULD kill someone if he wanted to. He isn't afraid. In the Three Garribeds, Watson gets shot by Killer Evans and Holmes says that if Watson had been killed, Evans wouldn't have got out of the room alive. And you have to believe him at that point, he's for real...

Sherlock enjoys hand to hand combat because I think he genuinely gets a bit of a thrill from fighting. He's trained in martial arts and boxing so why wouldn't he?

Thank you for this very smart post-- you know your stuff. And I totally agree with you; even though I've been roundly criticized for my opinions here, I don't seem to be able to drop it. Sigh. Sherlock is no stranger to violence, or to using his physical strength to manipulate others into saying or doing what he wants. IMO it's a short step from that to using a gun to slow someone down or kill them, if no other option is possible. I doubt Motiss or any other writers would have him kill mostly because a) it's not necessary and b) it's far better TV to watch him torture someone and make them scream (as what happened when S stepped on the cabbie's shoulder wound to make him give up Moriarty's name) than to just go BOOM and silence them.

If "M" was Mycroft - that would have really been a Scandal!

"Without you – without your assistance – we would not have found passage into London. You have my thanks."

Mycroft as the one to support a Chinese crime syndicate? Why would he be doing so?The Queen would not be amused at all and have him sacked at the spot.

Doubt it would have been Moriarty himself, so one of the snipers who are now targeting Sherlock's friends.

kazza474 wrote:

The whole essence of Sherlock Holmes is that he will never kill anyone. That is part of his mystique. This is part of the stories. The hero killing for any reason is part of other stories, but not this one.

Oh well, reading this from today's perspective and after His Last Vow. 

After looking this episode again, I got another idea who M is:
As Shan chated with him she said that she couldn't foresee that Sherlock suddenly appeared, but she observed John and Sherlock from the beginning and the only thing I can remember which could be  surprising for her was the visit in the circus and the fight with Sherlock and John. In this scene Sherlock unmasked the brother of Soo Ling and saw his face. So I thought this guy was perhaps M and after he was unmasked by Sherlock he felt insecure.