It is, as akenaton, says. There are sincere persons and groups who are offended by homosexuality and who, rightfully, see marriage as a religious ceremony. That's what comes from giving the clergy the authority to legalize a contract. In our society, which is, constantly, walking the tightrope between majority rule and individual rights, we compromise by giving the religions the power to marry but we don't give them the exclusive franchise. Also, we don't give them the power to break the contract.
Personally, I can't see what is wrong with civil unions. Gays, like oppressed minorities before them, deserve the same legal rights as anyone else. But, for goodness sake, let the religions keep their magic words. Even after civil unions are recognised, those churches who wouldn't marry gays, then, they sure wouldn't marry them now.
I agree with the akester about protecting rights of both sides. The disgust on the left makes the disdain on the right seem downright neighborly. There is, also, an arrogance and self rightiousness that assumes that everyone interested in folk music must be a Democrat.
That said, ake and his band of rightious christians will have to put up with things changing. They can pretend that it's 1947 and they hold season tickets to Ebbet's Field.

                      Mike