What reason does the Inspector give for appearance of deviations?

From the text:

The inspector took another sweet and pushed the bag back to me. '". . . and each foot shall have five toes,"' he quoted. 'You remember that?'

'Yes,' I admitted, unhappily.

'Well, every part of the definition is as important as any other; and if a child doesn't come within it, then it isn't human, and that means it doesn't have a soul. It is not in the image of God, it is an imitation, and in the imitations there is always some mistake. Only God produces perfection, so although deviations may look like us in many ways, they cannot be really human. They are something quite different.'