“Considerations Regarding Proposals To Give Legal Recognition To Unions Between Homosexual Persons” – Vatican, CDF, 2003

The Church’s teaching on marriage and on the complementarity of the sexes reiterates a truth that is evident to right reason and recognized as such by all the major cultures of the world. Marriage is not just any relationship between human beings. It was established by the Creator with its own nature, essential properties and purpose. No ideology can erase from the human spirit the certainty that marriage exists solely between a man and a woman, who by mutual personal gift, proper and exclusive to themselves, tend toward the communion of their persons….

There are absolutely no grounds for considering homosexual unions to be in any way similar or even remotely analogous to God’s plan for marriage and family. Marriage is holy, while homosexual acts go against the natural moral law. Homosexual acts “close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved”.

Sacred Scripture condemns homosexual acts “as a serious depravity… (cf. Rom 1:24-27; 1 Cor 6:10; 1 Tim 1:10). This judgment of Scripture does not of course permit us to conclude that all those who suffer from this anomaly are personally responsible for it, but it does attest to the fact that homosexual acts are intrinsically disordered”.

Christians give witness to the whole moral truth, which is contradicted both by approval of homosexual acts and unjust discrimination against homosexual persons. …

Those who would move from tolerance to the legitimization of specific rights for cohabiting homosexual persons need to be reminded that the approval or legalization of evil is something far different from the toleration of evil. …

In those situations where homosexual unions have been legally recognized or have been given the legal status and rights belonging to marriage, clear and emphatic opposition is a duty. One must refrain from any kind of formal cooperation in the enactment or application of such gravely unjust laws and, as far as possible, from material cooperation on the level of their application. In this area, everyone can exercise the right to conscientious objection. …

[T]he State could not grant legal standing to such unions without failing in its duty to promote and defend marriage as an institution essential to the common good. …

Legal recognition of homosexual unions would obscure certain basic moral values and cause a devaluation of the institution of marriage. …

Homosexual unions are totally lacking in the biological and anthropological elements of marriage and family which would be the basis, on the level of reason, for granting them legal recognition. …

It is one thing to maintain that individual citizens may freely engage in those activities that interest them and that this falls within the common civil right to freedom; it is something quite different to hold that activities which do not represent a significant or positive contribution to the development of the human person in society can receive specific and categorical legal recognition by the State. …

Because married couples ensure the succession of generations and are therefore eminently within the public interest, civil law grants them institutional recognition. Homosexual unions, on the other hand, do not need specific attention from the legal standpoint since they do not exercise this function for the common good. …

Legal recognition of homosexual unions or placing them on the same level as marriage would mean not only the approval of deviant behaviour, with the consequence of making it a model in present-day society, but would also obscure basic values which belong to the common inheritance of humanity. …

http://www.vatican.va/roman_curia/congregations/cfaith/documents/rc_con_cfaith_doc_20030731_homosexual-unions_en.html