In which case to avoid dragging the subjective moral values of some into the domestic arrangements of others wouldn't it be better to abolish civil marriage altogether and just have civil partnerships for anyone regardless of their sexual intensions, religious affiliation or lack of said?

That way a heterosexual couple of the Roman Catholic persuasion could have a church wedding and sign a civil document of union which is the same as the one a homosexual couple would sign if they announced their union a meeting of the Society Of Friends or at a ceremony of their own design etc.

That way the marriage would be a ceremonial rite of choice subject to whatever moral stance the organisation performing it may hold and civil union would a legal/economic contract with the state.