Morality is premised upon the status quo of a particular social or cultural group, in which a whole host of judgements and responses are bound up in it, in order to provide some order and relative understanding amongst the composite people in the group.
Morality is a human creation and therefore subjective. Different groups have different morality complexes with each hinging on a specific system of value. Each values a specific quality or achievement that molds the rest of the morality. They are all based on opinion and not fact, without validity.
Generally we can explain that A is good because of B. It count as a explanation because B is more fundamental than A. By repeating it, we can found the core of our morality, what a lot of philosophers had do. The problem is that we end up with different core moralities.
And because these cores are what they are, we have no more fundamental principles/values/things that would allow us to compare them.
There are intuitive universal moral imperatives that, when abandoned, lead to societal and individual harm. To kill robs a person of their life and it robs society of a human resource. Greed, rape, oppression, dishonesty, and violence are all universally immoral, regardless of cultural bias/view.