I agree. Everyone has the right to defend themselves. However, this case and so many others are due to legal contradictions. You have the right to defend yourself using, as the article says, "reasonable force". There has been a recent surge in the number of people in Europe who take self-defence classes of various kinds. Having been mugged once and threatened with a knife, I fully understand where they are coming from.
Unfortunately, the law is not black and white. Whilst you do have the right to defend yourself, you do not have the right to harm, injure or kill anyone. How do you interprete "reasonable force"? If someone breaks into your house and you surprise the burglar, how much force are you allowed to use? Does the mere fact that the man is invading your private domicile imply a threat to your personal safety? I have read of cases where people have restrained burglars with more or less violence and have subsequently been successfully sued by said burglar.
Another aspect is vigilantism. When does self-defence take the nasty turn into "society is not going to help me, so I'll help myself"? If we say that self-defence is acceptable, and I do believe it is, what do we tell people when they enquire how they should fight back against an armed man? Then you end up with people carrying knives around, just in case. Then someone gets the bright idea that they are not physically capable at winning an armed melee, so they resort to firearms instead. And, despite the trite cliche often invoked by the NRA, guns kill people. As do knives.
I fully support the individual's right to defend themselves but I also see the problem. When I was mugged and threatened, I got quite angry, went home and fetched a rather nasty and tremendously sharp sabre with the clear intent of finding the bastards and skewering them. Granted, anger, adrenaline and booze led to this stupid decision but luckily friends stopped me. If I had succeeded, I would have been a murderer. Had I then decided to carry a knife around and the police caught me, I would be treated as a criminal, since I was carrying around a weapon with the intent of using it should it be necessary or, to be precise, should a situation arise where I decided a knife would be needed.
This store-keeper should not be charged with anything but having the guts to stand up to one of those people who make normal people afraid to walk the streets at night.
However, what remains is the daunting and hard question: what is 'reasonable force' and what/who defines it? Does the meaning change according to the situation? How do you prove, like in this case, that the store-keeper used nothing more than 'reasonable force' seeing as the other guy is deceased and cannot present his side of the story?