This is a very fundamentalist concept of Christianity. Keep in mind that Jesus did not write the NT. Everything that he said, was stated to a crowd of fellow Jewish (and perhaps a few pagan) listeners. The Gospels record his speeches to other Jews. When he said that all of those who listened to him and rejected him would be judged by God, he was referring to the Jewish and Greek people who saw him and heard his words. I hardly believe this to mean that people on a remote island will be sent to fiery, eternal torment because they have never heard of Jesus. That's Dante's Inferno, not the Bible. For all we know, the people on that island may be better Christians than the rest of us. They may have had spiritual encounters with God in their own way.