For reasons to be reasons "they would have to justify anyone else (believing, valuing, or) doing the same in my place".
For someone like myself, who seeks to find reason inside (imminent within) rather than outside diversity, a great deal turns on how one goes about substantively and legitimately filling in the notions of "generality" and of being "in my place".
Not every position in the empirical world is a "place" in the sense that would support a claim of reason, although many positions are. That is one way to think about the difference between a "genuine" and a "spurious" culture, as the difference between a "place" that con support a claim of reason and a mere "position", which cannot. In a moment I will suggest that under certain interpretations of "place", reason can be made one of the foundation stones for a defensible anthropological relativism, previously because it is universally true that (for example) any person who is rational ought to want their marriage to be a arranged, if the are a young woman living in a rural Indian village. If one could in fact succeed at enumerating some good reasons - I think I could come up with a few - that would justify anyone wanting an arranged marriage who was in such a position, then one would have also succeeded at establishing the social position of young women in rural India as a "place" supportable by reason. It would no longer be merely a position to be understood solely in terms of the contingencies of power.
Relativism in anthropology is the attempt to show that certain forms of diversity can be rationally justified.
The aim of a true anthropological relativism is to show us how reason is compatible with genuine diversity in what people believe, value and do. If one is to succeed as an anthropological relativist one must start by carefully documenting the existence of diversity in some practice (e.g, love marriage versus arranged marriage, separate sleeping arrangement versus co-sleeping arrangement for children and adults, variations in the sexual division of labor and so forth) and end by being able to convince "anyone who is willing to listen" that what is done in that society at that time is done for reasons that no rational person should necessarily reject.
*Columbia University copyright 1995