Everything is expendable to a dalek including itself. They are the poster children for nihilism nothing has meaning. The emptiness of death means little when its basically the same as living. After the dalek is compromised, it begins to understand the difference. The image of the star being born fills a void inside that it didnt know it had. The Doctor tries to immerse the dalek in images of beauty and wonder but he is chasing a fallacy. He cannot hide what he is, and he is like all things both dark and light and everything in between. The dalek cannot recognize life without death or good without evil. The Doctor interprets the daleks decision to return to its fleet and destroy its former shipmates as a failure but is it? The Doctor has created a dalek in his own image. With morality comes responsibility. Its easy to say war is bad, but does that mean you should never intervene when atrocities are committed?