The only morale problem an employee would have with full disclosure of everyone's salaries would be for the pathetically poor performing employee. And frankly, nobody gives a damn if they happen to have low morale. That's the whole point. To discourage them from staying in your company and dragging it down, while encouraging them to be seeking a job more suited to their skills and temperment.

Everyone in the military and the government knows how much everyone makes. That provides a certain drive to better yourself to reach the next level with absolutely known rewards for success.