Well, I suppose a universal truth vis-à-vis an observable objective reality is good to know. For example, if doing A causes X suffering, while doing B reduces X's suffering, and it is always the case, then I suppose realism makes sense. Because then we could do B as an ethical decision, and we could avoid doing A for the same reason.
It's when we get into specifics that we run into problems. Nothing in ethics is formulaic (that I know of), which is why constantly observing reality is essential if you want to go that route.
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Knowing that death is certain and that the time of death is uncertain, what's the most important thing?
—Bhikkhuni Pema Chödrön
Humankind cannot bear very much reality.
—From "Burnt Norton," Four Quartets (1936), T. S. Eliot
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