God exists

The brain-tumor example still doesn't establish what you need it to establish. You are showing that our capacity to make moral judgments is physically dependent on the brain. I agree. But that is an epistemological/psychological claim, not a claim about what makes moral propositions objectively true. If a brain tumor causes someone to believe that torturing children is acceptable, that doesn't make torture objectively acceptable. It demonstrates that someone's belief about morality can be mistaken and causally altered. The distinction between moral judgment as a psychological phenomenon and morality in the normative sense is explicitly recognized in the philosophical literature. � Stanford Encyclopedia of Philosophy +1 Here's the crucial analogy: damaging someone's visual cortex can change their perception of color, but that doesn't establish that the wavelengths of light themselves are created by their brain. Likewise, altering someone's moral psychology doesn't establish that objective moral truth is created by their brain. Your second objection—that objective moral facts could exist as abstract, brute facts—is logically possible. But “could exist” is not the same as “therefore they do exist.” You have proposed a competing metaphysical explanation; you haven't demonstrated it. And notice what you're conceding: objective moral truths exist independently of human opinion. That's already moral realism. Contemporary metaethics recognizes naturalist, non-naturalist, and supernaturalist attempts to explain such stance-independent facts. � Stanford Encyclopedia of Philosophy +1 So the actual dispute is now much narrower: What best grounds objective normativity? If you say “brute moral facts,” you've stopped the explanation at morality without giving a reason why such irreducible normative facts exist. If you say “natural facts,” you need to explain how purely descriptive facts generate genuine obligation. If you say “abstract moral truths,” you still need to explain why these truths have normative authority over rational agents. The theistic proposal isn't “we don't know, therefore God.” It's an explanatory hypothesis: objective moral obligation is ultimately grounded in the necessary nature of a perfectly good personal reality. So your brain-tumor example doesn't defeat objective morality, and “maybe brute moral facts exist” doesn't refute the theistic grounding argument. You've established that our moral cognition has physical mechanisms; you have not established that objective moral normativity itself is reducible to those mechanisms.