I chuckled at the idea of using karate or a knife as self-defense against an armed attacker. Also, self-defense does not mean "shooting", it doesn't even have to mean taking the safety off. Lifting your shirt to reveal the handle can be enough to send a man with a knife sprinting in the other direction.
I'm not sure how many of you are from the States or not, but I can guess from this thread.
To those of you saying that he shouldn't get it because the solution to guns is not more guns: There's estimated to be 350,000,000 million guns in the United states. 200,000,000 of those are registered and legally owned by responsible, trained adults like our friend Zeeba here. That leaves 150,000,000 illegal guns, in the hands of criminals, who obviously intend to use them. There are 300,000,000 people in the United States. You do the math.
These guns cannot go away. The legal ones are protected by the Second Amendment of the supreme law of the land, the Constitution, and the illegal guns will obviously not just be handed over by the people who have them. They're just going to leave it where it is, hiding, because it's already illegal.
Guys, I'm a super-hippy. I play guitar and smoke pot(its not even illegal in small amounts in my state) and believe in freedom and love and happiness and all that bullshit. But, this is an issue that just needs to be looked at realistically- there are more guns than people here, and a firearm is an ideal self-defense tool, if not purely from necessity.
If there's a God, I hope he forbids you ever having to use it.