I think marriage should no longer be a legal issue. If you want you and your partner to be legally recognised (same-sex or hetero) then you should be able to get a civil partnership, which will offer the same legal rights as marriage does now. If you want to get married, either for faith reasons, tradition, or to make public vows, then you still can. Different Christian denominations (and other institutions/religious groups) can decide for themselves whether they want to marry gays. If they do, they are legally free to do so and are accountable to God. If they do not, they are legally free to do so and are accountable God.