Islam admits Mary was the virgin mother of Jesus.
Islam admits that Jesus was not born of Joseph for Mary was a virgin.
Islam admits that it was the miraculous spirit of God that conceived Jesus in her womb.
So Jesus is not the son of Joseph.
Jesus is the Son of God.
If he is not the son of God, who's son is he.
If you declare he has no father you declare the Messiah is a bastard??