How do Christians rationalize Job's children being treated like chess pieces?

I received this "question" from another user who defined immorality as "treating people like things", and must confess that I don't have a ready response. In the book of Job, God permits Satan to kill Job's children in order to test Job. While acknowledging the difference between direct action and permitting, it still seem very... questionable that God would allow other humans to be (ab)used in this manner. (Even more cynically, the user claims that the later children described at the end of the book of Job are 'replacements, as if Job's children are interchangeable'.) What is a (mainstream) Christian response to this objection?