Suppose that two gay men or two lesbian women wanted to get married, what kind of argument could a Utilitarian give on the subject? What kind of argument could a believer in Divine Command give? What kind of argument could a Kantian give?
From the point of view of Utilitarianism such a couple would not be considered utile. Despite the fact that in such a case maximization of benefits and reduction of the negative experiences might be undoubted, it is evident that a homosexual couple is not able to give birth to children, which makes their marriage inutile. On the other hand, such a family might adopt children and thus reduce their suffering.
From the point of view of a Divine Command believer such a union is inadmissible since it lacks the mystery of childbirth and contradicts the Commandments of God. From the point of view of Kantianism, a homosexual union is also not justified because it does not produce any moral worth and it is not related to the concept of internal duty that is deontological by its nature.