Krishna wanted his son to be exactly like Shiva. Shiva’s main function is to destroy creation. For his son to be like Shiva meant that the boy would be the cause of the destruction of his entire race. This was what Krishna precisely wanted because the Yadus could not be defeated by anybody. Immortality for humans is out of question therefore at the end of the Yuga the Yadus would destroy each other. Later Samba played an instrumental role in this.