
Originally Posted by
Telenil
Her doubts could have been enough for Mengsk to decide to make an example of her, instead of any other general. But if you stick strictly to her actions and behaviour, there was simply no reason to kill her there and then. She was not killed for what she had done or might do in the foreseeable future but, at most, because Arcturus thought she might reconsider her allegiance in a completely different situation. That's not pragmatism, nor a pre-emptive strike against someone about to challenge you - that's just turning on someone that is loyal to you on the ground that she might eventually prove dangerous in an hypothetical future. "Morally neutral" leaders don't kill people just because they have doubts but proceed with the mission anyway, if you are so amoral that being loyal to you is not enough, you are way into the evil zone already.
Now, Arcturus' actions make sense if you also factor that she was one of the ghost who murdered his family and that he was sending his troops a message - if you need a victim, you would choose someone who just objected about your orders over someone who didn't. But Kerrigan was not a threat in any way when she engaged the Protoss, and killing her didn't protect the Sons of Korhal against a tangible peril.