“But values are in the subjective realm. Any specific human brain is in only one person, therefore values are in only one person. Many are the philosophers and religious devotees who would have their own values mandated as objective. Personally, I think the attempt to do so is immoral.”Am I being objectively immoral or only immoral in the sense of your own subjective value standards? If subjective, I hope you are not trying to "mandate" your subjective values onto me.
I agree that values have a subjective element but some values are also based in natural law which is written into us as humans. Your argument has as it’s premise that humans are so different that there is no commonality to base any objective value standards. If you are right then on what basis can you tell anyone that they are wrong? On what grounds would you tell the early American slave owners that they were wrong for not valuing African American’s as equals. Most you could really say was that subjectively you value Africans American’s as equal but the slave owners would not be objectively wrong for valuing them less. They would be right based on their own subjective values.
You also have the problem that in a society that only has subjective values to base standards on, the only thing that makes something socially right or wrong is power. Might makes right which is scary.