What is the rationale behind this statement: "If management gets a union, it deserves one."
The point of labor unions is to represent workers in negotiations with management. Unions are most likely to arise in situations when workers feel that they need more from the management of their firm. This is the rationale behind the statement given.
Workers are, one can argue, most likely to form a union is they feel that management is not fair with them. If management is treating them fairly, they are not going to feel like they need a union to achieve a better deal with management. This means that a management team that treats its employees fairly is less likely to have its employees want a union.
In this sense, it is possible to argue that management that deserves a union gets one. If management would treat employees fairly, employees would realize that they are in a good situation. They would not feel the need to form a union to act as a counterweight to management. Whether this is true or not, this is the rationale behind the statement given in this question.