Yes on Proposition 8

A commission of the National Assembly of France, a country that allows civil unions but rejects same sex marriage, concluded that because the effect of same sex parents on child's developing psychological identity is unknown, such arrangements are not in the best interest of the child.  The language of the report recognized that "Marriage is not merely the contractual recognition of the love within a couple.  It is a framework with rights and obligations conceived in order to welcome and provide for his harmonious development."

The Church of Jesus Christ of Latter-Day Saints outlines the religious and societal necessity of preserving marriage in "The Divine Institution of Marriage" and emphasizes the same idea.

"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, through the ages governments of all types have recognized and affirmed marriages as an essential institution in preserving social stability and perpetuating life itself.  It is true that some couples who marry will not have children, either by choice or because of infertility, but the special status of marriage is nonetheless closely linked to the inherent powers and responsibilities of procreation, and to the inherent differences between the genders.  Co-habitation under any guise or title is not a sufficient reason for defining new forms of marriage."

David A. Bednar noted the ripple affect of not passing Prop8 would be a "tyranny of tolerance."  Not passing Prop8 takes away peoples right to believe in traditional marriage and allows for lawsuits to be filed against people and institutes who for religious reasons choose not to perform same sex marriages, not to perform in vitro fertilization for same sex couples, and not to allow adoption to same sex couples through their agency.  

I find it fascinating that only a few decades ago, the politic atmosphere was centered on not being "forced" to have a "piece of paper" to show commitment and believing that partners in committed relationships should have rights and protections.  California agreed and laws are in place.  Civil Unions are protected under the California Family Code.  Now the pendulum has swung again and the desire is to have that "piece of paper" that was not wanted or valued in the not so distant past.