No... it wouldn't "prove" or "disprove" anything. The difference between "objective" and "subjective" isn't popularity.
Intersubjectivity is used to determine objectivity. But I don't believe the moral law is subjective, I believe it is objective.
lets try this another way, is rape wrong?
is it wrong if a tribe votes it as right and does it anyway?
is it wrong if some countries think it is right?
YES, it is still wrong. This is an example of objective morality, versus subjective morality of say "killing is wrong" well this is subjective, but "killing innocent human beings is wrong" is objective, regardless of culture, religion, or race.
now does that mean that morality is both objective and subjective?
I don't think so, I believe the statement "killing people is wrong" is not a universal moral truth. So it is a category error using it. Only universal moral truths can be used as a litmus test for the question "is morality objective or subjective." Because it is only those truths that contain the 100% morality that we need.
in conclusion, we would only need one example to prove that objective moral truth exists, even if we only have 1. IT still proves that it is possible in the universe that objective moral truth exists.
now where does that morality come from?
we already proved it transcends all races, religions, and cultures.
and that is it is known by intuition.
Since it is known by intuition (through our conscience), and since no other animals even apes or chimpanzees (genetically 90-97% similar), have said morality (objectively speaking)
we can deduce this morality is from outside of ourselves.
according to talk origins large gorillas have brain sizes of 700cc, which is comparable to small humans.
Creationist Arguments: Brain Sizes
so why don't gorillas with nearly the same brain size have the same objective moral truth that we do? Chimpanzees are known to eat their own children for example.
Because morality is above ourselves, and it is inherent in our souls, animals who don't have souls will not have the morality that is from God. They have family instinct to take care of young etc, but not the morality we talk of that is objective above.
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Here is a quote from a book by norman geisler:
Lewis’ Moral Argument. The most popular modern form of the moral argument was given
by C. S. Lewis in Mere Christianity. He not only gives the most complete form of the argument
in the most persuasive way, but he also answers major objections. The moral argument of Lewis
can be summarized:
1. There must be a universal moral law, or else: (a) Moral disagreements would make no
sense, as we all assume they do. (b) All moral criticisms would be meaningless (e.g.,
“The Nazis were wrong.”). (c) It is unnecessary to keep promises or treaties, as we all
assume that it is. (d) We would not make excuses for breaking the moral law, as we all
do.
2. But a universal moral law requires a universal Moral Law Giver, since the Source of it:
(a) Gives moral commands (as lawgivers do). (b) Is interested in our behavior (as moral
persons are).
3. Further, this universal Moral Law Giver must be absolutely good: (a) Otherwise all moral
effort would be futile in the long run, since we could be sacrificing our lives for what is
not ultimately right. (b) The source of all good must be absolutely good, since the
standard of all good must be completely good.
4. Therefore, there must be an absolutely good Moral Law Giver.
The Moral Law Is Not Herd Instinct. Lewis anticipates and persuasively answers major
objections to the moral argument. Essentially, his replies are:
What we call the moral law cannot be the result of herd instinct or else the stronger impulse
would always win, but it does not. We would always act from instinct rather than selflessly to
help someone, as we sometimes do. If the moral law were just herd instinct, then instincts would
always be right, but they are not. Even love and patriotism are sometimes wrong.
The Moral Law Is Not Social Convention. Neither can the moral law be mere social
convention, because not everything learned through society is based on social convention. For
example, math and logic are not. The same basic moral laws can be found in virtually every
society, past and present. Further, judgments about social progress would not be possible if
society were the basis of the judgments.
The Moral Law Differs from Laws of Nature. The moral law is not to be identified with the
laws of nature. Nature’s laws are descriptive (is), not prescriptive (ought) as are moral laws.
Factually convenient situations (the way it is) can be morally wrong. Someone who tries to trip
me and fails is wrong, but someone who accidentally trips me is not.
The Moral Law Is Not Human Fancy. Neither can the moral law be mere human fancy,
because we cannot get rid of it even when we would like to do so. We did not create it; it is
impressed on us from without. If it were fancy, then all value judgments would be meaningless,
including such statements as “Hate is wrong.” and “Racism is wrong.” But if the moral law is not
a description or a merely human prescription, then it must be a moral prescription from a Moral
Prescriber beyond us. As Lewis notes, this Moral Law Giver is more like Mind than Nature. He
can no more be part of Nature than an architect is identical to the building he designs.
Injustice Does Not Disprove a Moral Law Giver. The main objection to an absolutely perfect
Moral Law Giver is the argument from evil or injustice in the world. No serious person can fail
to recognize that all the murders, rapes, hatred, and cruelty in the world leave it far short of
perfect. But if the world is imperfect, how can there be an absolutely perfect God? Lewis’
answer is simple: The only way the world could possibly be imperfect is if there is an absolutely
perfect standard by which it can be judged to be imperfect (see MORALITY, ABSOLUTE NATURE OF).
For injustice makes sense only if there is a standard of justice by which something is known to
be unjust. And absolute injustice is possible only if there is an absolute standard of justice. Lewis
recalls the thoughts he had as an atheist:
Just how had I got this idea of just and unjust? A man does not call a line crooked
unless he has some idea of a straight line. What was I comparing this universe with when
I called it unjust. . . . Of course I could have given up my idea of justice by saying it was
nothing but a private idea of my own. But if I did that, then my argument against God
collapsed too—for the argument depended on saying that the world was really unjust, not
simply that it did not happen to please my private fancies. Thus in the very act of trying
to prove that God did not exist—in other words, that the whole of reality was
senseless—I found I was forced to assume that one part of reality—namely my idea of
justice—was full of sense. [Mere Christianity, 45, 46]
above section from:
Geisler, N. L. (1999). Baker encyclopedia of Christian apologetics. Baker Reference Library (498–501).
Grand Rapids, MI: Baker Books.