If the GM Board of Directors unanimously approved a decision on the first vote, the company's legendary Chairman, Alfred Sloan, would never accept the decision. Sloan believed that a board comprised of intelligent, monumentally successful captains of industry could never instantly agree on anything. He required opposing views, believing better quality decisions result from honest disagreement.
Sloan’s belief is backed by considerable research. Ori and Rom Brafman write in their book, Sway: The Irresistible Pull of Irrational Behavior, group conformity is rarely good. Productive dissension leads to richer debate and better decision making. Playing the role of a devil’s advocate produces a healthier and more productive conversation and forces leadership to evaluate different options, identify potential threats and make more intelligent decisions.
There is the other side of the coin. Some people like to disagree simply to be disagreeable, and others don't like to be challenged regardless of how valid the opposing point of view might be. That's why the most effective leaders welcome opposing views but demand that they are presented in a civil, gracious and dignified manner. The opposition should not be personal or mean-spirited. The goal should be to disagree respectfully but ultimately support whatever decision is reached even if you don't believe it is the right thing to do.
Checking one’s ego at the door makes encouraging and profiting from opposing opinions possible. There’s a reason that there are written opposing and supporting positions for every Supreme Court decision. If you want to make better decisions, invite opposing points of view.