The correct answer is: " to lend credibility and additional support to their conclusion".
The author describes morality and economics as two opposing forces. He provides an example in which morality rules over economic incentives, which are described as the profit maximization prospects. In this case most people are governed by morality rather than by greed. Although, at first, it might seem a contradiction to economic theory, the author aims to reject this statement. To support this viewpoint, the author cites a publication by Adam Smith, one of the most important theoretical economists in history, where he already examines how the forces of morality govern human decisions and, in turn, how they affect economic decisiones and their outcomes.