Homosexual orientation is disordered, meaning it’s existence is not ordered with nature to the good of mankind. It cannot provide the physical, spiritual, psychological and biological complimentarity that heterosexuality does. It can not procreate, hence it completely thwarts the inherent drive to perpetuate the human species. It requires the misuse of the human anatomy in ways that cause harm to the body. It does not fulfill the two basic insticts of human sexual interaction - unity and procreativity. HOWEVER, same sex attraction, in itself, is not a sin. The sin is in the behavior alone. Men and women who believe they have a homosexual orientation yet live a chaste existence are in complete confomity with Church teaching, whether they identify themselves as “gay”. “SSA”, “homosexual”, or whatever word du jour is being used. Courage, the Catholic group that ministers to SSA individuals, suggests that certain words that are more closely associated with an active homosexual lifestyle (gay, queer, etc) should be avoided but there is no official teaching on how a chaste homosexual should identify themselves.
You might try reading the Catechism. I also found this book helpful:
amazon.com/Truth-About-Homosexuality-Cry-Faithful/dp/0898705835/ref=pd_bbs_sr_1/103-7097656-1600603?ie=UTF8&s=books&qid=1183434664&sr=8-1
Debating with non-Christians can be difficult. I don’t bother as I think we have our hands full just trying to help other Catholics understand. You could provide stats on the mortality rate, the disease factor, the anatomical component, etc. A great and helpful book on the issue of same sex marriage is:
amazon.com/Future-Marriage-David-Blankenhorn/dp/1594030812/ref=pd_bbs_sr_1/103-7097656-1600603?ie=UTF8&s=books&qid=1183434962&sr=1-1
For Christians, and Catholics in particular, it’s pretty simple. Our God, in His infinite wisdom, has allowed us to cooperate and participate with Him in bringing new souls to live here with us on earth until it is time to return home to Him. He provided us with a guide book and a manual on how to do this. We get married to someone of the opposite sex, we engage in baby making activity, always mindful of the privilidge we have in assisting God in the creation of more human souls. We stay married to our spouse for our whole lives to provide those new souls with the love, security and faith they need to go out into world and become saints. When we stray too far from the guide book and ignore what the manual says, we get into big trouble. And that goes for all sinners, not just one particular group.
I’m not a guy so I’ll pass on that one!