If society dictates moral motivation, then we have no right to criticize slavery, genocide, or anything. It is a product of their culture. Because morality is relative to each group. Evolution teaches all morality is merely a long development from animal instincts. There is no intrinsic sense of morality in people.
Consciences are thus no proof of a deity and are merely a result of an evolutionary process.
This is a two-edged sword. For it kills reason and the scientific method, also. The evolutionist believes that the human intellect also developed from the physical brain of Primates. Yet he assumes that intellect is trustworthy. If there is no God, there is no basis for morality .