If morality is entirely determined by social consensus, does a terrible act become morally correct if an entire society unanimously agrees it is right?

 If morality is determined by social consensus, then by what standard is an act terrible?

Either there is a category of ‘terrible’ that is outside social consensus, or social consensus determines what is terrible.

This is the problem with deciding what is terrible by social consensus. Is something terrible in and of itself, or is it only terrible because people have agreed it’s terrible? If everyone in a society agrees an act is not terrible, does that mean it’s not actually terrible, or just that no one in that society thinks it is? Meanwhile another society has decided, for whatever reasons, that that sort of behaviour is terrible.

Individuals will disagree, so where is the objective standard to adjudicate between two differing subjective evaluations?

Morality comes into play when there is a goal that a moral code is trying to achieve. So first the goal of morality has to be determined. Is it for the individual, the society, the nation, humanity in general, or all forms of life and the planet?

If there is no morality above what humans can conclude then anything can be considered moral or immoral if enough people agree. Even if no one agrees with one person's moral code, if it is logically consistent with the goal he has adopted for morality, then the fundamental disagreement is not about the logic of his moral code but about the goal itself.

If for arguments sake we define what is terrible as anything that prevents human flourishing, we haven't solved the problem. We have simply moved it back one step. What constitutes human flourishing? That depends partly on what we think a human being actually is.

From a purely biological perspective, human flourishing might be understood in terms of health, security, prosperity, freedom, relationships, psychological well-being, reproduction, and so on. If those are the ultimate measures of human flourishing, then thousands of species might become extinct or suffer enormously in the pursuit of that goal, without that necessarily being considered morally wrong. But millions of people understand the human being as having a spiritual dimension that cannot be reduced to the body. For them, flourishing may also involve the development of the self, spiritual knowledge, liberation from bodily identification, and a relationship with Krishna. And there are some of us who don’t think human flourishing should be at the expense of other harmless species.

So even if everyone agreed that preventing human flourishing is terrible, we would still have to determine what a human being is, what constitutes flourishing for that being, and what cost to other harmless species is morally defensible. Different answers produce different conceptions of what is terrible.

If terrible is whatever a society collectively decides prevents human flourishing, then I consider a morality that simply adopts whatever society collectively decides to be a terrible idea because I consider it an obstacle to human flourishing.