This memoir takes a response to fallacy as its title. Oranges Are Not the Only Fruit implies that the belief pattern she is opposing is one where one truth automatically discredits another one. Perhaps, the title is designed to suggest that her mother viewed truth with a closed-minded way, setting up her own beliefs as the only valid version of belief. This pits Jeanette against her own self, however, and it inverts the power structure in her home, because Jeanette knows from her experience of sexuality that her mother is wrong.
Her mother says that homosexuality is evil, and that gay people are sinners who will go to hell if they neglect to repent of it. But Winterson knows from personal experience that such beliefs are outlandish and wrong, but her mother is not lesbian, so there is very little young Jeanette can do to persuade her mother to love her for who she is. She has to wrestle with her mother's failure to appreciate her, alongside confusing, often shameful experiences of what should be very natural.
Without the religious view holding their family back, perhaps there might have been room for Jeanette to believe something similar but different from her mother, and then perhaps they could have enjoyed conversations about each other's points of view. But, ironically, the mother cuts off her source of communion when the issue of sexual morality and religion comes up, so the author has to take a consolation instead of getting what she wants. Instead of her mother's love and approval, she has to learn to give herself her own love and approval, until she is strong enough to believe in her point of view despite her mother's influence in her feelings of shame.
