Persuade Someone without a Reference to Religious Belief

Do you have any insight as to how I could persuade someone without a reference to religious belief that "only marriage between a man and a woman [should be] valid or recognized" by the state (CA Prop 8).

A month ago, I asked a question like the above of some friends. I strongly believe that "The family is ordained of God. Marriage between man and woman is essential to His eternal plan. Children are entitled to birth within the bonds of matrimony, and to be reared by a father and a mother who honor marital vows with complete fidelity." (The Family: A Proclamation to the World)

This morning I found The Divine Institution of Marriage. A document "to explain [the LDS church's] reasons for defending marriage between a man and a woman as an issue of moral imperative" I have not read it all yet. It has given me some points of reason that might persuade voters to constitutionally define traditional marriage.

The Church does not object to rights (already established in California) regarding hospitalization and medical care, fair housing and employment rights, or probate rights, so long as these do not infringe on the integrity of the family or the constitutional rights of churches and their adherents to administer and practice their religion free from government interference.

I agree with this. Defining traditional marriage is not about taking away civil rights.

Marriage is not primarily a contract between individuals to ratify their affections and provide for mutual obligations. Rather, marriage and family are vital instruments for rearing children and teaching them to become responsible adults. While governments did not invent marriage, throughout the ages governments of all types have recognized and affirmed marriage as an essential institution in preserving social stability and perpetuating life itself. Hence, regardless of whether marriages were performed as a religious rite or a civil ceremony, married couples in almost every culture have been granted special privileges aimed primarily at sustaining their relationship and promoting the environment in which children are reared. A husband and a wife do not receive these privileges to elevate them above any other two people who may share a residence or social tie, but rather in order to preserve, protect, and defend the all-important institutions of marriage and family.

I will probably post more as I read through this and gather other sources to support these propositions.

Here is a list of some of the public statements the LDS church has taken on Same Sex Marriage:

20 October 2004. "The Church accordingly favors measures that define marriage as the union of a man and a woman and that do not confer legal status on any other sexual relationship"
http://newsroom.lds.org/ldsnewsroom/eng/news-releases-stories/first-presidency-statement-on-same-gender-marriage

Last date noted: March 2005. Church Joins Other Faith Groups in Defense of Traditional Marriage
http://newsroom.lds.org/ldsnewsroom/eng/public-issues/church-joins-other-faith-groups-in-defense-of-traditional-marriage

24 February 2008. Care for the Flock. "On 23 February 2008 The Salt Lake Tribune posted an article about [Peter] Danzig who was a member of the Church’s Orchestra at Temple Square. According to the story, in June of 2006 Mr. Danzig published a letter-to-the-editor in the Tribune (and letters in other local newspapers) encouraging members to oppose Church leaders on the issue of same gender marriage."
http://newsroom.lds.org/ldsnewsroom/eng/commentary/care-for-the-flock

30 June 2008. California and Same-Sex Marriage. "The following letter was sent from the First Presidency of The Church of Jesus Christ of Latter-day Saints to Church leaders in California to be read to all congregations on 29 June 2008"
"We ask that you do all you can to support the proposed constitutional amendment by donating of your means and time to assure that marriage in California is legally defined as being between a man and a woman."
http://newsroom.lds.org/ldsnewsroom/eng/commentary/california-and-same-sex-marriage

13 August 2008, The Divine Institution of Marriage. "The California Supreme Court recently ruled that same-sex marriage was legal in California"
http://newsroom.lds.org/ldsnewsroom/eng/commentary/the-divine-institution-of-marriage

UPDATE 2008-11-03:
Some one sent me a link to a speech by Robert George, "On the Moral Purposes of Law and Government". He is a Professor of Jurisprudence at Princeton University.

I have not listened to all of it but I like it so far.