I am not going to say what the army did was right, or wrong. I wasn't there and have no right to condemn the actions. All I can do is try to give an explanation of the times and fears, I think the men were feeling.
I was in Ireland during "The Troubles," http://www.bbc.co.uk/history/troubles. I was stationed well behind the lines but at the same time, there was a fear of living in an occupied territory and being hated for being there.
I was in Ireland at the date of the Maze Prison hunger strikes http://www.belfasttelegraph.co.uk/opinion/columnists/archive/ed-curran/how-the-maze-prison-could-tell-our-labyrinthine-story-of-horror-29227984.html. I spent two months on our base and never went further than the mess. To go off the camp, you had to supply an account of what you intended to do and when you estimated to be return, for your safety.
I doubt if any of the modern Irish even know what caused the problem; for generations the Catholics hated the Protestants for just being different and vise-versa. At one point, there was a school built with and the pupils came from both sides, but it didn't last long.
How can a person sitting safely in London evaluate the situation of the soldiers in the streets of Ireland fearing for his life? In a war situation, a soldier has a split-second to assess and react or die. In a conflict where soldiers were getting bombs hurled at them at every corner from both sides, how can you condemn a man for firing on a person raising his arm? To that soldier, at that time, the person could have been waiting to throw a bomb.
I witnessed the hatred at first hand being an English airman on a Scottish naval base. A close friend was knifed walking from the bus stop to the base - the length of a football pitch.
By sheer luck, I am writing this today, on a journey from Holland to Germany the train I was in was shot at crossing the Dutch border. Only luck saved the bullet from hitting the driver and causing a major disaster. I looked down the barrel of a gun at the 1979 European Cup Final in Munich http://www.theguardian.com/sport/2009/may/03/forest-malmo-may-1979.
A similar thing happened to the soldier in My Lai in Vietnam http://www.history.com/topics/vietnam-war/my-lai-massacre. I've read about the war, and can tell you things that you probably didn't know. I won't go into the weapons used by the VC, they have little to do with the situation in hand, suffice to say they were designed to poison and debilitate as much as to kill.
The story of how the troops killed the villagers of My Lai is well documented, and yet all this was done in safety, not by people who were there and witnessed the horrors that preceded the event.
Before the killings, the troops had to endure listening to their comrades being tortured. The tortures were broadcast in the jungles by a series of loudspeakers, in between the screams the troops were bombarded by chants of "Yanks, go home!"
A typical scenario for the torture is to lash the men, and then when their skin is raw and bleeding through water filled with salt and god knows what germs all over them. Don't forget, like Ireland, any of the so-called civilians at My Lai could have been a VC soldier, in a guerilla war such as Ireland or Vietnam anybody can be the enemy. And they rely on this confusion of not knowing who is on your side to infiltrate camps.
We're acquainted with the photo of the young girl running down the road on fire - probably the most known image of the war - the first reaction is "Oh, poor girl." Stop, consider this alternate, and true, scenario. A med-evac chopper with a huge red cross sits idling full of dying troops; a young girl walks up to the helicopter holding her hat in front of her, at the last moment she pulls the pin and throws a grenade in the hatch. That scenario, no matter how repulsive to the reader - was a well-used tactic of the Vietcong.