I do realize now I accidentally shifted the language from "universal" morals to "objective" morals. If a moral principle is claimed to be universal, it must, by definition, be applicable to all possible scenarios.
An objective moral isn't invalidated by an immoral choice still being the most correct choice in a set, but a universal moral is invalidated by only a single exception.
I suppose it's up to you if you were agreeing with the OP on the choice of "universal".
If the hypothetical is “sterile,” it should be trivial to engage with. But to avoid shock value, take something ordinary like lying. Suppose lying is objectively morally impermissible. Now imagine a case where telling the truth would foreseeably cause serious, disproportionate harm, and allowing that harm is also morally impermissible. There is no third option.
Under an objective moral framework, how is this evaluated? Is one choice less wrong, or are both simply immoral? If the answer is the latter, then the framework does not guide action in hard cases. Moral objectivity is silent where it matters the most. This is where it is helpful, if not convenient, to stress test claims with even the most absurd situations.