Prop 8 supports... What kind of ******** argument is this?

A bunch of conservative and religious organizations have united last year to pass Proposition 8, which amended the California Constitution to define marriage is between a man and a woman, thus making "same-sex marriages" illegal. There was a huge media blitz left and right, and in the end the Right won. But one wonders why are these people so anxious to 'save' it from the same-sex couples?

If you read their brochure, you can figure out where they're coming from:

[The following is translation of a real Chinese brochure passed out during Prop 8 mania. ]