People may be able to avoid earthly punishment for their sexual indiscretions, but they can not escape God's judgment; an afterlife of eternal pain and suffering in hell. Religious sanctions of this sort are supposed to be in opposition to man's sinful nature; restraining his dangerous sexuality.
However, punishing others for sex is actually part of man's nature. In nature, sex is highly competitive. Dominant males fight and threaten as they try to control sexual access to fertile females. Human males behave similarly. Rather than being in opposition to human nature, religion actually reinforces man's "animal instinct" to control the sexual behavior of others. This explains why religion-inspired sexual restrictions and punishments are so popular among men.
Of course, religion claims that it's really all about morality. Without strict religious control over sexual behavior human passions would lead to the destruction of society. God has given us His law in order to protect us from ourselves. Religion, it is often said, is what is good for society. But if this is so, why is it that those societies where religious belief is strongest and which have the harshest penalties for breaking the sexual code are also the societies that tend to be the least orderly and the most corrupt, brutal and violent?
Religion is taken very seriously in many of the Islamic societies of the Middle East, and the strictest sexual code is adhered to. Yet, these societies are characterized not by prosperity and social order, but by poverty, violence and oppression.
Meanwhile, the most sexually liberal societies, especially those of Western Europe, are the freest and the most democratic, prosperous and orderly. If strict sexual morality is not really good for society, why do religious conservatives everywhere continue to clamor for it? And why do people so willingly accept religion that tells them their sexuality is sinful and shameful? The truth is that most of the time people act on their own selfish feelings and desires, not on what is good for society as a whole.
The desire to limit and control the sexual behavior of others is felt by women as well as men. Powerful feelings, such as sexual jealousy, inspire aggressive behavior. Strict anti-sex religious morality allows people to act aggressively on these feelings in a sociably acceptable way. Thus, it's not really about doing what is good for society, it's all about individual desires. This is best explained from an evolutionary perspective, which is exactly what this book does.