In an ideal world the HR department would be considerate of every employee's needs and there would be no need for unions. But in practice the incentive structur

In an ideal world the HR department would be considerate of every employee's needs and there would be no need for unions. But in practice the incentive structure of the HR department doesn't allow that, so you need a competing incentive structure to balance things out (the union). Neither can achieve the goal perfectly on their own.