There is so much more to family than simply the marriage of a man and a woman; however, that marriage is the foundation not only of the family, but of our culture and identity. The family structure offers stability, discipline, morality, structure, education, and much more. It is the foundation of our society and has slowly been destroyed as liberal groups have picked away piece by piece the family structure leaving not much of it left in the liberal wake of destruction. Promiscuity, abortion, single parenting, homosexuality, and government dependency have destroyed the family structure and delivered in its stead lifelong poverty, instability, behavioral disorders, mental problems, and a slew of other problems that will keep the offspring relegated to a life of misery. Proof beyond a reasonable doubt? Any kind of tampering or destruction of traditional values and/or culture, regardless of sexual preference, will have a injurious impact on society. There is no proof otherwise except for the rewritten "history" by various groups looking to come out of a subculture and declared "normal".
As to civil unions, this has ALWAYS been on the table since "marriage" was suggested; however, gays have an agenda. They're really not interested in their love for each other or sharing their lives. Their real interests (the gay lobby) is to reinvent society and force the liberal agenda of promiscuity, abortion, single parenting, homosexuality, and government dependency down our throats at whatever costs.