This is related to philosopher David Hume’s distinction between IS (facts, reality) and OUGHT (duties, morality)
However, I would like to introduce some nuance.
It is not that red pillers are morally relativists. It is impossible to be morally relativist, because each person has a concept of right or wrong (for example, «pleasure is right and pain is wrong»). Is it wrong from married men to be destroyed in family courts only because women want another cock? Whether you answer «yes» or «no», you have a concept of absolute morality.
It is that red pillers have different opinions about morality. So you find everything: from Orthodox Christians (like NovaSeeker) to complete hedonist PUAs. From reactionaries that dream of a return of the Ancien Regime to left-wing people (like Jayman). I have even seen some Muslim men from time to time. Some people (like Roosh) drastically change their complete moral framework.
It is that the red pillers gather together to discuss facts and not morality. Then, far from the manosphere, each red piller applies these facts to his life (this application needs a personal morality).
More importantly, red pillers thinks that facts are independent from morality. So if something is true, it is true even if it is immoral. By contrast, blue pillers think that if something is immoral, it is false. So they go from OUGHT to IS, from morality to facts. For example, «men and women ought to be equal» becomes «men and women are equal». This is known as «the moralistic fallacy» and it is the basis of the West after the Enlightenment. «All men ought to be equal» becomes «All men are created equal».