Does a moral value go from being subjective to objective if it begins as the idea of a single person and eventually becomes universally accepted?
If I convince the world I have six fingers on one hand does that change the fact that I have four and a thumb?
If you convinced me, you have six fingers.
I'm a rational skeptic and an empiricist. I may provisionally accept your claim that you have six fingers on one hand, but I won't accept it as a fact - that is, I won't be convinced - without seeing your hand and maybe an X-ray of it as well.
Now that I've answered your question, did you want to address mine? I thought it deserved a little more consideration than the six-fingered comment.