After writing that post, I actually did think of something that might fit the criteria of being morally wrong.
If an individual knows the consequences of an action to cause suffering or death but does not inform those who they know are likely or about to engage in those actions, there is complicity in the consequences. It is true that the consequences, suffering and death (which you, James, mentioned before) are considered wrong based on prejudice, but if we can consider that the suffering would be of a certain kind (intense physical suffering from loss of limb, for example) that either everyone would be against, or else at least the subject who would engage in the behaviour which would result in such a consequence, is averse to, there is a sense of responsibility on the person who knows the consequence that the other might not be aware of…
That knowing subject might say they thought the other should know the consequence, which may release them from their obligation, but particularly if that knowing subject also knows that the acting subject would result in a harm that that subject would be averse to and knows not of, there is what can be called a moral lack.
But, I still think to enforce any moral obligations would necessitate conventional agreement and enforcement. It does not need to arise as a natural moral category within the individual (in this case the “knowing subject”)— something implanted by nature.
The problem that I find with this line of reasoning though, is once you begin to say things like, any action on the part of an individual to cause known suffering on another is morally wrong, the lines begin to become really fuzzy as the reasoning is taken to an extreme. Which is still why I say it is safer to say there is no morality in nature, morality is part of convention. That doesn’t mean we wouldn’t like, or think good, these conventions, but it is still a created category and not something that exists objectively in nature.
Because the purpose of an ethical system is to define what is needed for “the good life”. And though a community of moral conventions may be considered good to many, certain conventions may impinge on what is considered the good life to certain individuals. It is for that reason why I think there is no true overbranching objectively based morality — ie. no one size fits all morality that could define what is a good life for every individual on earth. The creation of the good life must come from the actions of each individual on their own behalf, and even then it is uncertain — this is again why I ultimately reject an objective moral category.