"Can't you lead a good life without believing in Christianity?" This is the central question of "Man or Rabbit?" C.S. Lewis makes two conclusions: first, that a good life in godly terms is impossible for anyone, and second, that living a good, moral life is not the goal of our existence.
One problem that I had with Lewis in this essay is that he is once again dealing only in extremes. He talks about only Materialists and Christians and no one in between. What happened to all of the other religions? Where do they fall? Can't a Hindu or a Buddhist live what anyone would consider a good life? We must not see only the two extreme cases because our lives do not involve only extremes. We spend most of our time in the middle ground, dealing with people who might be trying to be "good."
This brings me to my second issue with this essay. What definition are we using for the word good? According to Lewis, we must be using a biblical definition of good works, as in good coming from God. I agree that this is the true definition of good. I also agree that as sinners, we can't live a good life in a biblical sense. However, if a person actually is asking this question, I'm sure that they are not thinking of good in a biblical sense. Instead, they are thinking of basic moral practice. In this way, I would argue that in a way, people can live a good life in worldly terms outside of Christianity.
Notice that I don't think that this morality can earn them salvation. Salvation comes from the cross. If God has mercy on others who have never heard, that is wonderful. We can hope for the salvation of the unbeliever without access to the Gospel, but I don't think that we can assume that it will happen.