I'm a Christian.
I believe that Jesus is God in flesh, the only savior, the only provision of God for man's sin.
Islam would tell me I have committed shirk (شرك ). It's the unpardonable sin of associating anyone with God.
I get that. But I truly believe the bible teaches that Jesus is God, the second person of the Trinity.
On many theological issues I disagree with Islam dramatically. I know the issues. I have taught courses on Islam. I have read much of the Quran and studied it to know what Islam teaches.
I really love the Muslim people. They are, for the most part, sincere passionate people of faith. To the best of their ability they are living for and obeying the God they know.
So why would I, a Christian, insult Muhammad? Why would I say something negative about a man my Muslim friend considers a prophet of God? How would those statements help me relate to another person I believe God really loves?
I wouldn't! I couldn't insult their prophet. It serves no helpful purpose except to inflame and divide even more. I truly believe that God loves the Muslim people and many millions are finding Christ as savior each year. God is working with these sincere God seekers...he's drawing them to him.
For me, a Christian, to insult a man they revere would only grieve the God I serve. Instead, can I tell you more about my wonderful savior, Jesus Christ?
He is so amazing, so wonderful, he loves you and cares more for you than you will ever know. And, as the Quran says, one day he is coming back to judge the world. Can I tell you more about my wonderful Jesus?