The way I see it, terms like 'good' and 'bad' are only meaningful in relationship to a society in general. Societies flourish because on average, people contribute enough to them for everyone to be able to reap the benefits. You have people who provide food, people who provide tools, people who provide leadership to keep the whole thing running, etc etc. But if you have a nitwit in there that keeps randomly killing the farmers, he risks starving everyone. So killing productive farmers is definitely a bad thing. On the other hand, nourishing a sick person increases that person's chance of survival, so you decrease the odds that you lose manpower. So caring for the sick is a good thing.
So all of this kind of reflects back on what people expect to get in return for being part of a society: food, shelter, protection from harm, intellectual stimulation, video games, ... Actions that help the society provide these things are "good", while things that inhibit or harm society's ability to provide these are "bad". It might be a bit of a cynical view, but I don't think there's any other way to objectively rationalize any kind of morality. But then again, a question that comes to mind is "Is it good/bad/moral/just to rationalize morality?", and we're off to paradox land.