You know why i find this argument - not just what you said, but the whole entire arguement about the morality of his actions - stupid? His other two options were to execute him without a word, or tell him he was going to die anyway.
(EDIT: Or not kill him, which is the stupid idea.)
The first option would be called into question because somebody somewhere would point out that he said nothing and therefore he never even considered that the goblin could help, making it racist and/or evil.
The second would have put the goblin into a veritable state of paniced terror before he died, which is the state he ended up in anyway, making it evil and/or racist.
I only said that because somebody put his actions on par with Belkars, which you just pointed out is ridiculous.If that makes him better than Belkar in your eyes, then fine... the commander is less evil than someone whose level of evil is measured in kilonazis and has been compared to the fictional offspring of Sauron and Cruella DeVille for the sake of having a a baseline.