an eyeball that doesn't work

The other night Cade asked me why blind people can't see. I wanted to give a simple answer so I just said that sometimes people are born that way or sometimes they get hurt and it causes them to go blind.
What he really wanted to know was why do they have eyeballs if their eyeballs can't see. He asked me what is wrong with the eyeball that makes someone not be able to see out of it. I had to go a little deeper to explain about the optic nerve and how if it gets injured then the brain can't communicate with the eyeball and make it see. He was satisfied with the answer but thought that if someone's eyeball doesn't work then they should just remove it. Then I told him how people might make fun of someone if they were missing an eyeball. Cade thought that was so rude. He thought "no one should make fun of them, Mom. If it doesn't work then they don't need it so the guy without an eyeball should just tell them mean people that."
Very interesting... the mind of a 6 yr old little boy!