Gay marriage does not harm heterosexual marriage
The California Supreme Court states in their decision that “the exclusion of same-sex couples from the designation of marriage clearly is not necessary in order to afford full protection to all of the rights and benefits that currently are enjoyed by married opposite-sex couples; permitting same-sex couples access to the designation of marriage will not deprive opposite-sex couples of any rights and will not alter the legal framework of the institution of marriage, because same-sex couples who choose to marry will be subject to the same obligations and duties that currently are imposed on married opposite-sex couples.” Page 11. California Supreme Court decision (.pdf)
The most common causes of divorce in heterosexual marriage, according to family law experts are poor communication, financial problems, lack of commitment, dramatic changes in priorities, and infidelity. 2 Marriage equality will not affect any of these conditions in heterosexual marriages. Within our own church community, thousands of LDS families have been formed and then destroyed because of counsel that homosexual people should marry members of the opposite sex. When their sexual orientation is not changed by marriage, both spouses and any children suffer. See for example, Carolyn Ball, returned missionary, MTC instructor, relief society president, BYU professor — and homosexual — discusses her failed struggle to fight being gay in this video: “It doesn’t go away”.