Not just this but if what is morally correct is different to each person (subjective morality) then everything is arbitrary and societal agreements upon behaviour =/= why I should follow them, to assume this in your position as you have done is to assume a logical non-sequitur. In order to say certain behaviours are right and should be mandated, or even to ascribe any value to specific behaviours at all, is to require a basis on which these actions and their causes can be evaluated. Which obviously under subjective morality is impossible to construct and in order to do so you would need to assume a moral standard (something not relative).
You've made the mistake of saying that because morality has a cause therefore it necessitates certain actions be committed based upon that cause, to re-iterate the OP again "agreements upon behaviour =/= why I should follow them" especially if I'm the ultimate and only arbiter of moral truths (not really truth but belief, subjective truth is a misnomer see:
the comment you yourself responded to). To add to this, just because there is subjective interpretation about morals it does not mean that morality is subjective. Disagreement on belief about what the truth (or correct morality) is =/= that truth (or morality) is subjective, if it was the case there's no point in discussing any disagreements at all as we're both "true/correct".
Specifically you're also incredibly blind here and highlight the issue and why I'm saying nobody is engaging the OP because it refutes this exact thing:
I know you've read a bunch of the posts where I was speaking with Brad and showing him this very error, you responded to some.
In order to call these things good or bad you have assumed a moral stance and in order to justify it as a moral stance you will assume other moral stances, a perpetual circle. Within your worldview your very foundations here for saying "it's good morality has evolved to embrace justice" don't exist. That's the point. You're determining things to be good and bad without any justification. Even if that justification is survival, in order to call survival good you need to unfoundedly ascribe (assume) value to human life (hence why Materialism & Naturalism is mentioned).
"You're assuming an inherent value to survival that's unable to be substantiated.". I'll re-iterate here because I know what's coming as a response and I'll remind you
"because morality has a cause it does not therefore necessitate certain actions be committed based upon that cause". The explanation of morality's cause
(Edit: morality's cause within your worldview/paradigm) does nothing to condemn murder hence why in the thread title there is the word authoritative. In order for something to be right, like every other single truth, it needs to be universal and exist independent of belief (e.g rocks will continue to exist after I die even if I don't believe in them). Which as you know if a moral stance is universal then it's not relative/subjective.
To ascribe value to survival is to assume an unsubstantiated thing that within Naturalism & Materialism is unable to be substantiated.