Advocates of practices as diverse as wife swapping and homosexual relationships have made the argument that because they were born with certain biologically-based urges, it is morally acceptable, even morally laudatory, to act on those urges. For example, some homosexual advocates argue that if homosexual orientation is biologically based, then homosexuals cannot be morally blamed for acting sexually upon that orientation.
Let me present a similar argument. Heterosexual men are biologically programmed to spread their sperm to as many available women as possible. Men, from a biological point of view, are not monogamous but polygamous. Therefore, men should act on their sexual urges and have sex with as many available women that they can seduce. This is true for unattached single men, attached single men, engaged men, and married men. All should act on their biological urges.
Although as a man with normal male drives, the prospect in that previous paragraph is tempting, the problem is that following my urges would be destructive to myself and to others. The same is true of other men. They have a moral responsibility to be sexually responsible and not act on their biologically-based urges, no matter how powerful they might be. In order to rear children in a stable environment, male biological urges must be controlled and channeled in a monogamous relationship. The man may want sexual relations more than the woman; this is natural, but hopefully the couple can compromise and find a mean between extremes. As for total refusal of marital rights–that is considered legitimate grounds for annulment even in the Roman Catholic Church.
Why do humans have biological urges that are not morally right to indulge. Some Christians believe that one aspect of human sinfulness is a reversion to basic animal instincts, which then must be mollified for the purpose of creating a stable human society. As rational animals, we all have the ability to control our biological urges. The task is difficult. Sometimes people slip up. But as long as they keep up the struggle and do not lapse into the decadence of promiscuity, there is hope for them and for society. A society in which all males fulfilled their biological urges to have sex with as many women as possible would not long survive.
Thus, from the fact that “Person A has a biological tendency to perform act x” does not imply that “It is morally right for Person A to act on his (or her) biological tendency to do action x.” Such a nonsequitur is a commonplace in today’s culture wars. Moral discipline is called “discipline” for a reason. May God gives us the strength to have it and practice it, and may God forgive us when we fail. What is not open to us morally is to justify immoral activities in the name of biology.