I think that management's primary apprehension about labor is the fear of having profit margins lessened. As previously noted, management has had a tradition of being skeptical of the union's claims as being seen as ploy to cut into management profits. This doubt casts a pall on much of the negotiations and workings between the two. Both sides see the other in a light that might cast aspersions from one side to another. When management criticizes workers, it comes from the point of view of both authority figure as well as protector of profits. As a consequence, it becomes accustomed to the fact that labor and workers will openly criticize it on these grounds. Additionally, if management has to be responsive to share holders and other vested interests, it might have to devalue the perceptions of the labor force to a certain extent in order to maximize its own professional and economic viability. As with labor leadership, a tight rope is walked in certain contexts.
As with my previous answer, I think that a lot of the problem here is tradition. Management has come to see labor unions as obstructionists who care only for the workers and not for the health of the company.
However, I think that there is another reason going on here as well. The issue here is that management, on a daily basis, has to supervise labor. The management has to act as boss and disciplinarian. Because of this, it is hard for them to want to cooperate with labor. Managers, therefore, might object to cooperation because it would break down the barrier between boss and worker. If this barrier is broken, it might make it harder for the bosses to supervise and discipline workers in the way that they need to.
This is sort of like the divide between students and teachers, parents and kids, and (military) officers and enlisted.