“Equal marriage”: Is There A New Christian Ethic for Sex and Marriage?

Are Christian supporters of same-sex marriage simply extending the traditional teaching about sex and marriage to same-sex couples and what would that look like? Or are they – as seems to be the case with most secular supporters – simply welcoming the rectifying of an injustice which now gives gay and lesbian couples the same options to choose from in relation to structuring their relationships as straight couples have had for some time?