Please see my previous response and, in particular, this paper. In short, there is no moral calculus through which one can prove that moral behavior is correct. Moral Rationalism (the idea that morality is based on reason or rationality like calculus) isn't supported by the observable evidence.
To that I would add, morality requires that one care and there is no rational reason to care about anything that could convince a person who doesn't care that they should care. This is why psychopaths are all but impossible to cure or reform. They don't want to be cured and don't care and there isn't a rational argument in existence that can replace what they innately lack.
“In short, there is no moral calculus through which one can prove that moral behavior is correct.”
Do you understand what hubris you demonstrate by declaring something with neither a logical or factual basis?
Do you believe human beings have a specific nature that makes immoral behavior self-destructive? That is what your Bible teaches. Why would you not believe it.
Even Paul understood that moral values can be understood from nature.
Romans 2:14-15 “For when the Gentiles which have not the Law, does by nature the things contained in the law: these having not the Law, are a law unto themselves, which shew the works of the Law written in their hearts, their conscience also bearing witnesse, and their thoughts the meanwhile accusing, or else excusing one another ...”
If moral values have no practical consequences, than they of course cannot be known rationally. The Bible, and all rational men know, moral values have practical consequences, and are determined by the nature of the world in which we live, and the nature of human beings.
If moral values are not based on the nature or what human beings and the world are, then they are totally fictitious, like any other set of phony “principles” any conman wishes to press. Moral values are based on facts, the facts of what human beings and their nature is, and what the nature of the world they live in is.
Any principle that cannot be discovered by examination of reality and reasoning from those facts is not truth at all, but superstition.
Sorry that you and Paul are in such disagreement.
Hank