A person is smart. People are dumb, panicky dangerous animals and you know it. Fifteen hundred years ago everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. Imagine what you'll know tomorrow.
Yes the quote is from Men in Black, but still apply it's lesson. Today we KNOW that the only way to Heaven is Christianity and through Jesus. But before it wasn't necessarily true. Prior to Jesus' birth, people went to Heaven. We condemn people for not believing in Jesus. 2000 years from now, what's to say there's not going to be a new "alternative" to God that will be discovered?
Back when Jesus first died, would you have believed him if he was a man who said "Oh, I'm the Son of God". Or would you have believed in God as your family did for generations prior to his death?