I actually kind of like it. I like Sherlock's dark side.

Tinks wrote:

The cabbie had brought about the deaths of 3 innocent people and was quite boastful about this.
I don't like too much brutality either, but Moriary went on to kill other innocent people so I don't think Sherlock wanted his name just to feed his own ego.
I think he was justified in what he did - just about.

 
I think that it is worth noting that the cabbie had killed three people for money, and presumably would have carried on killing until his aneurism caught up with him. I doubt that there were ever chances of him picking the 'wrong pill'; think of cardsharpers ensuring that the game is fixed.

I agree that Sherlock inflicted pain, but inflicting pain is not always evil.

For example, I have spent my life having pain inflicted upon me for the best possible reason; without it I would have died. It still hurts just the same though. So I have no problem with Sherlock' s actions; he is acting in the role of necessity to spare more lives....

It didn't make me particularly uncomfortable. I may be a bit desensitised considering that I have plenty of experience in inflicting pain on people with or without their consent. In most cases it's in the best intrest of the person that is being 'hurt'. However there are times when we do unpleasent things like injections to individuals becouse we need to protect others. I would say that there is a long way from forcibly giving someone an injection to inflicting pain in order to extract information but there are some pararels in the ethical thinking behind those decisions.

Obtaining the name was important. Having the name of the boss allows Sherlock to address the route of the problem. Otherwise what would stop Moriaty from getting another 'cabbie' to carry on with the work. Inflicting pain on the cabbie could have potentially helped to save many people in an indirect way. It's a bit of a grea area in my opinion whether it's justified or not.

Ethics aside it made good TV. The touch of a dark side adds another dimension to Sherlock's character.

But Sherlock doesn't appear to do anything with the name he gets. He just seems to wait around for Moriarty's next move, which results in TGG. So what did he want it for? Future reference?
And in TGG Sherlock isn't even sure it is Moriarty behind it until at the end.

I too sort of like his dark side...

I think it was Sherlock's impatience; he had to know and he had to know now and didn't care about the cabby. He was dying anyway so I suppose in Sherlock's mind he was just a source of infomation that could be rattled like a money bank when you try to get a coin out.

Yes it bothered me and I have to look away every time...I honestly cannot watch any violence.
But I reasoned it with:  but he was gonna die anyway and he may as well do something useful before he does!
Maybe Sherlock could have asked nicely...
But would it have got the same result?  I dunno.

Let′s face it the cabbie was a scum who gleefully poisoned four people. Three people were in the prime of life, enjoying successful careers and one was just a young man on the verge of adulthood, practically a child. If Sherlock not only stepped on cabbie′s bleeding shoulder but kicked him to his head or clawed his eyes out, it would be rightfully delt – the scum deserved every single bit of it.
 
John seems to be quite meek and nice when compared with Sherlock, yet what does he says about the cabbie on his blog? „Frankly, after everything that man had done to those innocent people who got into his car, a quick death like that was better than he deserved.” Let′s not forget it was actually John who shot the cabbie and even when he came to know the cabbie was unarmed after the deed, he lost no sleep over it.
 
Sherlock was never deliberately cruel to some innocent or weak people. But he makes it no secret that he couldn′t be bothered to spend his compassion on perpetrators of such beastly crimes. He refuses to be seen as some saintly hero exactly for that reason.
 

It was brutal but I think justified because the name of the organiser of the crimes might have been one he knew and if he got the information he could go after them and it would prevent more needless deaths and pain. He maybe has that sense of justice ticking away in the background even then, it is Machiavellian but he's dealing with a cabble who kills to get money for his kids without a thought for if his kids would like to discover their father is a cold-blooded killer. Asking nicely didn't get a result, using force was necessary and there was no time to waste. Moriarty kept himself hidden until he was ready to reveal himself so the name was a mystery but Sherlock didn't know that as he forced the cabbie to spill it. He deals with killers and they are killers who don't care about the consequences of what they do until they have to face the consequences of their actions and own them. Magnussen caused Lord Smallwood to kill himself, so the end result is the same Magnussen killed for his own purposes. But Sherlock knew what the consequences were of killing Magnussen. The difference is Sherlock always tries to use words and reason first but he is as violent as necessary to be on the side of the angels.  .

And did they ever specify what kind of angels does he side with?
You can muder half of London if you are on the side of these :

http://www.pinterest.com/pin/144044888056094930/