Once again, you believe universality must be objective and that is incorrect. There are a few moral rules prevalent in every human society.
Not answering the question is not a profundity, it is weakness. When, among society, would it be "right" to do such a thing? As we go along we'll eliminate such items as "The man is a monster who predates children" until we have a simple code that is prevalent in every human society.
Thus stripping it of its facade to its central core... It is what we are working on right now. Cypress found some, can you?
So, with Cannabalism and "others" we find that the "morality" tends to limit itself to an "us them" mentality, as society grows ever "smaller" by communications and speedy travel we find that that includes more daily. Only isolated groups consider it an "us and them"...
However, even in those groups, if they have contact with the outside, we find that they hide and commit the acts rather than openly work their nefarious deeds thus evincing that even among those there is that fundamental inside belief that what they are doing is "wrong"...
Even terrorists wear masks to hide their identities knowing what they are doing is "wrong"..
Lets work with Cypress' Native American example. As we grew in society and learned through communication and because of quick travel we now view those Natives as "us" and believe it was wrong and is wrong to allow such action...
So, now we know the rule pretty much covers "us", So now we need to reword the question...
When would it be okay for somebody considered to be "us" to be murdered in cold blood?