I understand the original poster asked about same-sex marriage in regards to the Catholic Church and I don’t what to take this thread away from the topic questioned, but i just thought I would add that if you or anybody else is interested in reading or watching regarding what is marriage and arguments from a more secular perspective against same-sex marriage, please check out the following:
Ryan T. Anderson - What is Marriage?
Ryan Anderson Q&A “What is Marriage?” revised
What is Marriage? Man and Woman: A Defence - Sherif Girgis, Ryan T. Anderson, and Robert P. George
The Secular Case Against Gay Marriage
A Secular Case Against Gay Marriage
What is Marriage?
Harvard Journal of Law and Public Policy, Vol. 34, No. 1, pp. 245-287, Winter 2010