Deimos was quiet for a very long time. He hadn't thought of himself like Harmonia in any way, he just cared about her. He hadn't ever thought about what he did on the same level as what the other deities did; he just basically did what he was told, and didn't think twice about it.
But Zeus was pointing out--encouraging, and if you wanted to look at it honestly, almost ordering--that he had as much responsibility in his sphere of influence that Harmonia had in hers. That was an entirely new consideration for him, and he didn't quite know what to think about it.
"So you're saying that fear isn't just natural but necessary, to be influenced in all kinds of ways both positive and negative?" Because a positive use of fear, like the scenarios Zeus had mentioned, hadn't occurred to him. "And that even the smallest bit of fear or lack of it can be something in my influence?" He meant it as a statement; it came out as a question.