I think its merely a comparison that is used to show how wicked, those who criticize the Christian religion is, something for which they are extremely ignorant and in profound darkness.
The contrast is drawn with Michael the Archangel, who had all right to dispute with the devil over Moses' body. Why? Michael was obviously knowledgeable, and obviously doing the will of God. But Michael simply rebuked the devil.
Now wicked unbelievers have no right whatsoever to criticize and blaspheme the Christian religion, yet they willingly do so, hence showing the depts of their unreasonableness.