What does the Church really say about homosexuality?
(In response to a reader's comment):
Too many Christians - including many Catholics - put the cart before the horse and insist that Biblical reference is the standard of truth ... yes, it is... but what is true was true before it's inclusion in Sacred Scripture, and not only because of it's inclusion - make sense?
Your questions about homosexuality are quite valid too, in our society which teaches that tolerance is actually acceptance, and which dismisses the idea of absolutes - in the moral realm or elsewhere - as archaic.
The Church's stance on homosexual behavior (note: the behavior, or the action, being the locus of the sin, and not the desire itself, nor the person suffering the attraction) stems from the reality that we as human persons are created in God's image to love as He loves: totally, faithfully and fruitfully.
All moral and theological arguments aside, the stark biological reality is this: homosexual "love" can never be fruitful, and so it cannot rightly be called love.
The Church isn't trying to prevent people who struggle with same sex attraction from finding fulfillment/happiness/companionship ... she (the Church) is simply unable to teach something that is false. She will never recognize the validity of homosexual "marriage" because no such thing exists.
Marriage is, by nature, the permanent, fruitful union of two persons: a man and a woman, united in sacramental purpose for the begetting and education of God's children and for the mutual sanctification of each other. The Church won't change her stance on this because she can't. She didn't create it - He did.
We exist to be in communion with one another - to give and receive love so fully, so completely, that in the giving and receiving an entire other person may come into existence... much the way the Holy Spirit, though co eternal with the Father and the Son, is nonetheless an outpouring of the Father's love for the Son, received and returned with such perfection that the love, in essence, becomes an "Other." This Trinitarian exchange of love is mirrored - dimly - in the conjugal act between husband and wife, whose love can also incarnate, or make physical, the reality of their spousal love.
Kinda heady stuff for a comments section, but it is what we profess to believe as Catholics, and not simply because it is in the Bible or because it is socially acceptable at some juncture in history.