Onanism: What the Bible Actually Condemns. Few passages have been more misunderstood in church history than Genesis 38:8–10. Onan, Judah’s son, refuses to fulfill his duty toward Tamar, and the Lord strikes him down. For centuries, this passage has been used to condemn masturbation or all forms of birth control. But what does the Bible actually say? A careful look shows that Onan’s sin was rebellion against covenant duty, not simply the physical act itself.