If we are discussing a logical proof of ethics, its truth value does not depend on everyone agreeing with it.
Certainly. 2+2=4 no matter what people think about it. And if there can be a logically consistent theory of ethics, then the rules of that ethics are also immune to opinion. I just have some doubts there can be such a thing. I also have reservations, assuming there can be such a thing, that Stefan's UPB is it. In fact, if it does disallow "revenge" under all circumstances (which I have seen no proof of, but will research further), that would increase my doubts about it, because I don't find that to be a reasonable rule. I can give an example why:
Say you looked out your window, and saw a man you don't know plant an axe in your daughter's head, while she was playing in the back yard. She falls over dead. He then walks away; his violence is over, and there is no longer any need for immediate defense. However if he gets away, there is difficulty in DROs actually identifying him. Oh, and you have a rifle at hand. What do you do?
I think the answer is, "pick up the rifle and kill him". Yet you (I think) would call that immoral according to UPB. If that is truly what UPB says, then I have no use for it, and few people would. Are we all saying 2+2=5? I doubt it; I think UPB is saying 2+2=5. But I need to really find out if UPB calls that immoral...