Our culture tends in many ways to be skeptical; many, if not most, people today doubt that there is any truth upon which all individuals can agree. We are also relativists, thinking that morals are relative to a culture or even to an individual. In general, we don't believe we can know for certain that any actions are intrinsically immoral. In fact, our legal system prohibits actions traditionally understood to be immoral, such as murder and theft. Our laws, in fact, limit human behavior in many ways -- mandating, for example, that our children be educated or telling us which drugs are legal or illegal. These laws are based on a combination of what we believe is moral and what is beneficial/harmful for human beings.

Skepticism and relativism are very much behind the tendency of our culture to accept same-sex unions. Add in the fairly universal acknowledgement that human beings need to love and be loved, and it has led many people to come to the conclusion that homosexual unions should be tolerated and even approved. It seems arrogant to insist that homosexual unions are wrong and cruel to deny a segment of the population the opportunity to love and be loved.

Yet virtually all governments have had laws against homosexual unions, although some states have begun to extend the institution of marriage to homosexual couples. While it is mainly religious believers who retain objections to homosexual unions, there is a case to be made against homosexual unions that is based upon natural law, or a common-sense reading of reality. The same common-sense judgments that lead us to make laws that reflect basic morality and protect people from harm should lead us also to refuse to give legal recognition to homosexual unions.

Natural law argument

With the help of some rough analogies, let me demonstrate how natural law, or common-sense reasoning, operates. Two claims will be made here: 1) that there are some obvious truths and 2) it is relatively easy for people to know these truths; indeed, it is strange and problematic if people don't know them.

For instance, most people know that to get the best out of something it should be treated in accord with its nature. We observe that tomato plants need good soil, the proper temperature and amount of sunshine, and water to produce the best possible tomatoes. We know what children need to become healthy adults: love, nutrition, shelter, education and physical activity.

There is, of course, variety in these universalities -- different species of tomato plants will need somewhat different care, and children in different cultures will need different kinds of education. Still, the universal needs exist. Anyone who knows anything about tomato plants or children knows certain truths. When we see a wilted, dying tomato plant, we know there is something wrong with it; when we read of parents who lock their children in closets for years on end and nearly starve them to death, we know there is something wrong. When reading of such parents and children, we do not simply say that the parents have a different and unusual method of parenting.

Let us note that every sane human being acknowledges that there are natural love relationships that should not be sexual. Parents love their children; children love their parents; brothers and sisters love each other; teachers love their students; doctors love their patients. Traditionally included in this list is the love of same-sex friends for each other.

We also recognize that some people have appetites for sexual relationships that are not good: adults with children; living people with corpses; human beings with animals. States have generally made such unions illegal. We do not believe that those who say they can find love only in such relationships should be permitted to have them.

On the other hand, governments in every culture have given legal recognition to heterosexual unions. They have given recognition to them, in part, because heterosexual unions are the natural way for men and women to relate; it is natural for males and females to want to make a lifetime commitment to a relationship that, by nature, is ordained to bringing forth new life. The family is the cell of any society; it is the natural and best institution for raising up children to be able citizens of a society.

Natural relationships morally conducted bring great benefits to those who engage in them. Although no marriage is perfect, studies show that those who commit to heterosexual unions prosper physically, psychologically and financially. In fact, one indication that an activity is unnatural is that it is harmful for people. Unnatural unions are destructive of the individuals who engage in them; witness the number of infections, some of them lethal, transmitted through promiscuity, both heterosexual and homosexual. For instance, promiscuous heterosexual relations are very damaging; promiscuous individuals suffer such harm as unwanted pregnancies and abortions, and children born out of wedlock face a high chance of living in poverty and struggling in many other ways.

Inherently harmful

There is a much higher incidence of mental-health issues for those living the homosexual lifestyle, among them, a higher incidence of depression and suicide. Studies have found that homosexual males have a lifespan that is, on average, as much as 20 years shorter than the heterosexual male. It is only a slight exaggeration to say that heterosexual relationships morally pursued bring about life, whereas homosexual relations as generally conducted are aligned with disease and death.

In fact, there is much evidence that many of those who experience a homosexual orientation have been seriously wounded in their lifetime. Many of them suffered sexual abuse in their childhood. Others had troubled relationships with their parents; for instance, many males who experience homosexual desires report they were abandoned, neglected or abused by their fathers.

While many homosexuals profess to want the kind of relationship that married heterosexuals have, there seems to be something inherently unstable about such relationships. More than 75 percent of heterosexual males in committed relationships have been faithful to their partners; no more than 4.5 percent of homosexual males have been faithful to their partners.

Marriage brings benefits not only to the spouses involved, but also is clearly a benefit to the children they may have. Studies have shown that children prosper with the presence of both a mother and a father in their lives. The witnesses of those who have been raised by gay or lesbian parents in homosexual relationships indicate that they do not provide a healthy environment for those children.

Fundamental truths

Our culture does not seem to grant that it is obvious and easily known that homosexual unions are not good for human beings -- that they are not in accord with our nature. Why don't some people know these things?

We must acknowledge that human beings can get confused about fundamental truths, particularly if their culture teaches against these fundamental truths. For example, many visitors to Rome have encountered Gypsy children who are very aggressive pickpockets. Their parents tell them that it is right for them to steal. (The fact that the parents likely justify that teaching by telling their children that society generally cheats Gypsies indicates that they know stealing is wrong!) Whole cultures, of course, have accepted slavery as legitimate. Sometimes it requires brave and tenacious individuals to point out to a culture that it is violating some fundamental truths.

Some people claim that they do not need to live in accord with nature; that their lives, indeed their bodies, are theirs to do with what they want. After all, many people smoke and overeat, and the government does not prohibit them from doing so.

Yet, we must note that governments take measures to discourage people from smoking, such as taxing cigarettes and legislating that packages of cigarettes have danger warnings on them, and the U.S. government requires that the nutritional value of food be noted on packaging.

The argument can very reasonably be made that the dangers of homosexual sex are sufficient to warrant governmental measures to discourage such behavior. Abstinence-based sexual education programs are an example of governmental programs to discourage immoral and harmful heterosexual behavior.

Some people claim that laws denying marriage to homosexuals are discriminatory; that they are similar to laws that prevented members of different races to marry. We must note that not all discrimination is wrong; we do not allow all those who want to marry to do so; for instance, we do not allow those who want polygamous relationships to marry, or let adults marry children.

It is not simply a religious judgment that such relationships are wrong; indeed, it is a natural law judgment. Any person who understands human nature should be able to understand that such relationships are wrong. Since we consider such relationships to be wrong, we do not believe we are engaging in unjust discrimination when we forbid such relationships. To give legal recognition to such relationships would tremendously confuse the populace. Why are these immoral relationships legitimized and not others?

In their nature?

Some homosexuals claim that they were born that way, that God made them homosexual; they believe a genetic basis would mean that homosexuality is "natural."

No evidence has ever been found to establish a genetic basis for homosexuality. But even if it were found, this does not mean homosexuality is natural and moral. People are born with all sorts of conditions and tendencies that are not "natural." For instance, some babies are born without bodily parts; some people are born with a tendency to violence. In both instances, we would want to restore these individuals to a natural state; we would love to give limbs to those without them and to transform those who are violent into gentle human beings.

The fact that infertile couples are permitted to marry leads some to claim that homosexuals should be allowed to marry. There is, however, a world of difference between sexual acts that are by their very nature ordained to procreation or new life and acts that have no such ordination.

Heterosexual couples are doing something that has a natural purpose, although for some that natural purpose cannot be fulfilled. Homosexuals are engaging in acts that have no natural purpose, and in fact, because they have various health and other dangers, work against various natural goods.

Some people argue that it is unnatural for adult human beings not to have sex. The fact is, most people most of the time aren't having sex -- even those who are married. Most of us need to practice self-control of our sexuality most of the time. Morality requires that all heterosexuals who are not married should not be having sex and that those who are married should have sex only with each other.

As noted above, there are many kinds of natural love relationships. Indeed, while it is true that most heterosexuals will marry, it is not true that all of them find their strongest and truest and most intimate loves within marriage. Many spouses love their children more than each other; many spouses love their friends or parents or grandparents more than they love each other.

Let us hope that those who experience homosexual desires will learn to find love that does not harm them and others.

Called to chastity

While the Catechism of the Catholic Church affirms that homosexual tendencies are "objectively disordered" and contrary to natural law, it makes clear that people with such inclinations must be treated with respect and compassion. Still, people with same-sex attraction are called to live chastely.

Through chastity and "by the virtues of self-mastery that teach them inner freedom," the Catechism reminds people with homosexual tendencies that they "can and should gradually and resolutely approach Christian perfection" (No. 2359).

Related reading

Here are one book and several studies detailing the risks -- physical, mental, emotional -- and health problems associated with homosexual behavior.

"Meaning of Marriage: Family, State, Market, and Morals," edited by Robert P. George and Jean Bethke Elshtain (Spence, $29.95)

"The Slippery Slope of Same-Sex Marriage," by the Family Research Council: www.ctfamily.org/Slippery.Slope.Of.Same.Sex.Marriage.pdf

"Homosexuality and Mental Health Problems," by N.E. Whitehead on the National Association for Research and Therapy of Homosexuality website: www.narth.com/docs/whitehead.html

"Homosexuality and Hope," by the Catholic Medical Association: www.catholiceducation.org/articles/homosexuality/ho0039.html

"Health Risks of Gay Sex," by Dr. John R. Diggs Jr.: www.catholiceducation.org/articles/homosexuality/ho0075.html

Janet Smith holds the Father Michael J. McGivney Chair of Life Ethics at Sacred Heart Major Seminary in Detroit.