When it comes to things, utility may be the as far as it goes. Now that you bring that up I think people disagree on what is good because they really mean the utility of a thing and not morality. So when someone says being healthy is good and someone else disagrees there is really a disagreement about what health is good for. And when people disagree about the status of killing, the same thing is happening.
The difference between utility and morality is that utility is concerned with earthly things and morality is concerned with goodness itself. But goodness can be abstracted from things, which is why I like to start from things. Knowing what's good can inform action beyond what just knowing what's good and what it's good for.
I'd say goodness is what makes something good but I understand that is circular. You could just ask again what makes something good or what is goodness.
What do you think goodness is?
What do you think is the difference between utility and morality?