He doesn't explicitly intend to placate her; he thinks her distress has a real and understandable source. But his instinct is ever to deescalate, to bring the tension down and return to a ruthlessly practical way of looking at potential solutions. It won't do Hayley any favors, in his mind, if he treats her crises less seriously than he treats his own.

Bruce leans against the arm of the couch rather than sit when he sees that she isn't going to, and the surprise is clear in the lines of his posture when she finally clarifies. "Superman?" he repeats, vaguely incredulous. "Why would you-- that's dangerous. Absurdly dangerous. Even if he did-- wait. What do you mean, after his powers killed people?"

Somehow he hasn't been informed of this tidbit yet, and finally, at last, some of that dark dissatisfaction, simmering anger, is visibly lurking in his bearing. Bruce is quick. He has a suspicion about who's deaths she's referring to if she was worked up enough about it to attack someone practically invincible, and he doesn't want to believe that he could've missed a piece of information so critical.