Morality is composed of three things: good, evil, and fairness.
Some things are considered to be purely evil. If a person tortures another person as a way to make that person subservient or take pleasure in their pain, this would be considered evil.
If a person helps another person without the expectation or demand of gaining love or some kind of reward other than harmony, this would be considered good.
People have a proclivity to feel consciously torn when they do something evil and to feel serene when they do something good. I believe we could call this our collective subconscious instinct to live in good standing with one another, for whatever reasons you want to say (since the reasons will be subjective).
Everything else I think can fall under the system of fairness. People do what they think is fair. The businessman that works very hard in a capitalistic system and found success from it will find it unfair if others try to cheat that system. But others might see the fact that they work hard and have not had the success that the businessman had as then perfectly 'fair' to cheat the capitalistic system. I think this can also be applied to religions as well. We could look at someone following a religious belief and see that the judgments they impose on others are fair to them because their religious beliefs are the system that they have created for fairness that all human beings are supposed to follow. We can even apply this to the moral disgust idea that was presented in an older thread. When people find something disgusting, they don't see it fair to support such a thing, because they themselves find it disgusting. They may even think it is then fair to eliminate or try to stop something they think is disgusting just because it disturbs them and may believe it is then unfair to have to be subjected to that. In fact, I think all conflict outside of good and evil conflict comes from the idea of fairness; it is when different contradictory systems of fairness are created that conflict arises.
Then to create an infallible model of morality that someone can apply to any situation, must one then find a way to create unity between to contradictory systems of fairness? Is this theoretically possible? Or is it wiser to create a model that understands unity should not or can not be given in certain situations where tensions will not be relieved without conflict (in the worst cases war), but seeks it otherwise? Then are some systems of fairness destined to have to defeat another to exist?