What are the best refutations of the idea that moral facts can’t exist because it's immeasurable? To start off with, I don't think immeasurability is a condition for non-existence of moral facts. For example, your thoughts exist while also being immeasurable. A lot of aspects of the human live are immeasurable, but do exist (even if it's in a transcendental way).
I believe we (human species) have adopted moral values in order to create a stable, harmonious society, as a kind of attitude framework, to not live in absolute chaos where everyone would do as they please. Throughout our history, our numbers have grown and so has the need for moral judgement.
The classic ways of defining morality (objectivism, relativism, emotivism) are highly debated.
The big problem lies in formulating moral facts that count for everyone living on this planet. Because just because 90% decide something is morally wrong, doesn't make it morally wrong as a fact, a certainty. Very likely, but not 100% certain. Then, there is also the addition of intent when doing something morally right or wrong, but that is a completely other discussion.
Anyway, those are my 2 cents. I would like to add I'm a beginner in philosophy and English is not my native language, so pardon any mistakes.