Can guns protect people's lives?

I wonder if guns can really protect people.

I oppose to the idea that people should have weapons such as guns because people sometimes make a mistake.

Years ago, a Japanese student was shot to be killed by mistake in the United States in the Halloween night. He entered someone's property to ask the way to his friend's house, not understanding the word "Freeze!" and was shot by the property owner. 

If the owner had not had a gun, he wouldn't have to die. I wish guns were prohibited among ordinary people.