Alexander Lucie-Smith keeps the trick going:
A parliament could legislate that we should all drive on the left hand side, or the right hand side, as appropriate. Some countries have changed from one side to the other: but what side of the road you drive on is purely a matter of convention, human convention. Is what marriage is also purely conventional, in other words, whatever we decide it shall be? Our parliamentarians seem to think so, but on this matter they surely cannot be right. Even after any such proposed legislation becomes law, reality will be the same, nothing will have changed.
Natural law precedes human positive law, as some would put it. Human positive law cannot change natural law.
And you have access to this metaphysical truth how, Sir? If it was laid down by your deity, may we see the evidence? Where is it written in the stars that a seemingly social institution grounded in love is in fact necessarily exclusive of homosexuals? Or is it so obvious that we can all discover it by simply reflecting on our conscience, or by reading between the lines in your beloved Bible?
This would be an interesting debate to have on your own terms. But you’re not asking for a discussion at all. It’s mere assertion designed to get people to shut up and listen, and drink up your dogma as if it were infallible.