The is-ought fallacy (Hume) is a real fallacy, and is why knowledge is justified, true belief (Plato). In order to be knowledge, a belief must both be justified by the evidence, and true by
correspondence. If we consider justified a belief that only corresponds, we commit the is-ought fallacy. If we consider a belief true merely due to evidence in favor of it, we commit the ought-is fallacy.
Related to moral truth–if a justified (answering the question of Ethics–“How and why should we be or behave with the Other and self?”) moral standard doesn’t describe anything in reality, to consider it “true” commits the ought-is fallacy. If we take something from reality and call it moral truth, neglecting to consider whether it is justified (answering the question of Ethics), we commit the is-ought fallacy. In order for there to be moral truth, it must both correspond to (a) real being, and it must be justified (answering the question of Ethics). Its correspondence is not its justification (is=/=ought), and its justification is not its correspondence (ought=/=is).