On either of these definitions, it becomes impossible for someone in the group we are talking about to object to the dominant view or the view of the majority. 

For example, suppose I was in a group in which the dominant view or the majority view is that "X is good." Now suppose that I said "X is not good." That would be equivalent to saying "X is not considered good by the dominant view or the majority." But on our hypothesis that would be false.

The point is that if we define good in this way, moral criticism of the dominant view or the majority view becomes impossible. But we all believe that such criticism is commonplace.