Richard Gale presents the following argument to show that objective moral truths are not the sort of things that could be created.
(1) God determines the truth-values of ethical propositions.
(2) God is essentially benevolent.
(3) God is omnitemporal, i.e., his eternality involves beginningless and endless duration in time.
(4) God is benevolent prior to his decision as to what truth-values ethical propositions will have. [From (2) and (3)]
(5) Nothing is good or bad, right or wrong, prior to God's decision as to what truth-values ethical propositions will have. [From (1)]
(6) Therefore, it is impossible for God to exist. [From (1), (2), and (5)]