"Civil unions" = "gay marriage" with a different label.
The label is important, making the distinction between those couples of the procreative sort and those couples with same-sex attraction disorder. Marriage is a child-based institution; civil unions are purely for the selfish interests of the disordered couple.
Civil unions would not be just for same-sex couples, but for any combination of couple regardless of relationship. A brother and a sister; a divorced mom and her son; two brothers, etc....