The argument would probably resemble an agnostic position, I. E. Objective morality might exist, But it can never be known. Thus the only morality that can be known is subjective. Other than that I am just as lost as you.
The people who are saying that an objective standpoint of morality could never be known are creating self-defeating statements. To claim something can't be known is to create a claim that attests some sort of knowledge of that particular thing.
@thetaboosun I agree with that. I would also include genocide and rape. Maybe murder as well, But there are exceptions. Murder is legally defined as the “unlawful killing of another human being”, But it depends on the context. “Unlawful” is a relative term, So there are situations where it is legitimate to kill another person. But it does not apply to rape and genocide.
When people say morality is subjective, They are partly right. But they’re wrong when they say it’s all subjective. Morality has three parts or determinants: the act itself, The intention and the situation/circumstances. Motives are subjective and circumstances are relative, They’re always changing. But the moral law is objective. Common sense tells us all three parts have to be good in order for the act to be morally good. Three popular modern ethical systems emphasize just one factor and disregard the other two; legalism says only the objective act counts, Emphasizing the objective moral law and disregards the motive and circumstances. Moral subjectivism concentrates on the subjective intention while ignoring the act itself and circumstances, And moral relativism says everything is relative to the situation.