Recently, there have been some writeups on E2 which touch on the topic of homosexuals and Catholics. There seemed to be a bit of inaccuracy in the writeup so I wanted to write a general node on the topic to clear up any misunderstandings.
Before I start, I should mention that this is not intended to be a condemnation of anyone in a homosexual relationship, nor is it a statement about Catholic moral superiority. This is simply a factual summary of teachings by the Vatican which Catholics should strive towards. In addition, these teachings are all built on the foundation of love for neighbour/love for God and should reflect that in everyday life. If you ever happen to see me or another Catholic contradicting these teachings, please do us a favour and remind us of what we profess to work towards. Finally, I write this as a non-authoritative source on the matter. I am deliberately avoiding the topic of homosexual marriage because I don't think I know enough about the teachings to accurately represent them. I will write it up at a future date. There is a good chance there are factual errors present in the document despite my best efforts and if you catch them, please let me know.
A bit of background
Catholic teaching on human sexuality, which encompasses everything from homosexuality to contraception, is rooted in God's love for creation. This love is most profoundly expressed through the Jesus' sacrifice at the Passion. Pope John Paul II and Pope Paul VI ensconced these teachings through their works The Theology of the Body and Humanae Vitae respectively. Over the course of his 129 sermons on Theology of the Body, JP II stressed the principle of loving the other person totally and eschewed the concept of using someone to satisfy personal desires (including non-sexual desires).
The teaching about Free, Total, Faithful, Fruitful arise from these works. To determine whether a person's love reflects God's love for creation, it must be freely offered, total, completely faithful, and fruitful. Jesus' sacrifice at The Passion is often cited as an example of Free, Faithful, Fruitful, and Total love.
Free: Is love given without conditions? Jesus' sacrifice was offered freely to everyone without conditions.
Faithful: Is love offered even in times of tribulation? Even in the garden of Gethsemane, Jesus did not abandon his love for us.
Total: Is love all encompassing? Jesus offered everything even to the point of his own life for us.
Fruitful: Does the love bear fruit? The result of Jesus' love for us was the salvation of all humanity.
Catholics view Marriage and other aspects of human sexuality under this lens. A prostitute cannot offer love as God offered it because it is not Free, nor Total. Pornography is also not loving because it is not Free, Faithful, or Fruitful. Marriage can be loving because it has the possibility of fulfilling all four components. (Here I feel the need to reiterate that this is an ideal towards which Catholics strive, not something that we claim to have already attained.)
Given that we have covered a bit of the motivation behind the Church's teaching on sexuality, we can now hope to tackle the original issue.
Homosexual acts
The Church distinguishes between the homosexual act and the homosexual tendency. In fact, many Catholics dislike the usage of the term 'homosexual' because it implies defining a person solely on their sexual orientation. Instead, the terminology 'homosexual tendency' or 'homosexual attraction' is often used. A person with homosexual tendencies is someone who feels attraction to members of the same sex. The homosexual act is defined as engaging in homosexual behaviour (intercourse) with a member of the same sex.
The Church does not condone the homosexual act for the reason that it does not have the possibility of being Fruitful. This position is often somewhat understood by the general public. However, it is important to note that the Church does not disapprove of the homosexual tendency. The view of the Church is that experiencing homosexual tendencies is beyond the control of a person and therefore not morally disordered. It is not until a person with homosexual tendencies decides to act (or not to act) on their urges that a moral question arises. To make this more concrete, we can use an analogy. A smoker may have an urge to smoke, but this urge is only the desire to do something. He or she has free will in deciding, although it may be difficult, whether to smoke or not. Therefore, the person with irreconcilable homosexual tendencies is called to enter a life of celibacy. Although this seems harsh under some philosophies, entering a life of celibacy (irregardless of having homosexual tendencies) is a regular occurrence in the Church. I should add that celibacy does not necessarily imply priesthood or life in a convent.
Another teaching, seemingly often misrepresented within popular culture and sometimes forgotten by Catholics, is that even if a person is participating in a homosexual relationship, it does not preclude God's love for them, nor does it preclude a Catholic's obligation to love them. Homosexual acts are one type of sin which a person may commit and does not carry any special significance with it (other than the fight to legitimize it). Finally, I should mention there are communities for people who experience homosexual tendencies but wish to live chaste lives within the Catholic church. One such organization is called Courage.
Courage - http://couragerc.net/