"Imam Hussein and Preserving the Monotheistic Tradition by Translating It into a Demand for Justice and Dignity"
Had Imam Husain paid allegiance to Yazid, the message of God would have been entirely lost. Husayn was the representative of the line of tawhid, purity, honesty, and obedience to God. If he paid allegiance, the people would have been completely confused and gone astray.
There would have been no hope for guidance afterwards. However, Yazid was determined to have the allegiance of Husain. He pressured Walid, the governor of Medina, to have Imam Husain pledge allegiance (bay‘at). This facilitated the event of Karbala whose roots go back to the time of the demise of the Prophet, if not even earlier. In response to Yazid’s demand, Imam Husain replied to the governor of Medina: "O governor! We are the People of the Prophet’s House, and we are descendants of the Prophet. Yazid is a drunkard who murders without reason, and a person like me does not pay allegiance to a person like him."
It is not a matter of personal battle, but rather a matter of two separate ideologies. How could Husain give legitimacy to Yazid and become his follower? Allegiance would mean that Imam Husain and his followers would become Yazid’s followers. This means the end of Islam.
The next morning, the governor’s deputy found Imam Husain at the grave of Prophet Muhammad and advised the Imam to pay allegiance because it was safer for his life. Imam Husain replied, “We belong to God and to Him do we return. If Muslim nation is to be ruled by a leader like Yazid, say goodbye to Islam. I have heard from my grandfather, the Messenger of God, say, ‘Caliphate is forbidden for the family of Abu Sufyan.’
Source: IMAM HUSAYN THE HEIR OF PROPHET ABRAHAM: By Mohammad Ali Shomali [Vol. 1, p. 14-15].