The first such personality is Imam Ahmad bin Hanbal. He is quoted by Imam Dhahabi in the latter’s book, Mizaanul I’tidaal, Chapter Four, page 440, to have said: “Yazid should not be accepted as a narrator of any Tradition.” Besides that, Imam Dhahabi himself on the same page (where he quotes Imam Hanbal) says, “Yazid’s trustworthiness is questionable. Therefore, no Traditions should be accepted from him...” There you are! Can such an unreliable person ever be regarded as Amirul Mu’minin?
Not only did Imam Hanbal forbid people from accepting any Tradition from Yazid, but he also cursed Yazid, in his book Al-It’haaf Bihubbil Ashraaf, pages 63-64 for killing Imam Husayn (a.s).
The second scholar is Sheikh Muhammad Abduh. In his exegesis of the Holy Quran called Tafsirul Manaar (Volume Six, pages 367-368), after explaining how Yazid opposed Imam Husayn a. s., he says, “May Allah forsake him (Yazid) and all those who supported him, and those who have hatred for Imam Ali a. s; who continue to worship the oppressive rulers in their opposition to the establishment of justice and the religion of Allah...”
The third source is Imam Shawkaani. In his book Naylul Awtwaar (Volume Seven, page 362) after criticizing those who blame Imam Husayn a. s. for opposing Yazid, he curses both Yazid and his father, (Muawiya) in these words: “May Allah curse them”. Then, commenting on these blames, he says, “O my Lord. Just hearing such things is blood-curdling, and could shatter mountains.”
Imam Taftaazaani is the fourth person to talk on this issue. He is quoted in Irshaadus Saari (Volume Fifteen, page12), a commentary of Sahih Bukhari, to have stated that the consensus among scholars is that it is permissible “to curse those who killed Imam Husayn a.s., and those who ordered, or allowed or approved his murder.” Then having said that it is a common knowledge that Yazid approved the killing of Imam Husayn r.a. and the dishonouring of the House of the Prophet (S), he adds, “May Allah’s curse be on him (Yazid), his helpers and his associates!”.
The fifth person to expose Yazid was his own son whom he named after his father, Muawiya. He took over Caliphate on the death of his father, Yazid. But his reign was short-lived since he abdicated forty days after his succession or, by other accounts, five months after his succession. At the time of his abdication, he went on the pulpit and gave an address in which, among other things, he talked about the feud between his grandfather (Muawiya bin Abi Sufyan.) and “one who was better than him and every body else (meaning Imam Ali a. s.). He then mentioned his father (Yazid) and “all his evil deeds”, and “that he did not have the qualities befitting a Caliph of Muhammad’s community”; he then described his father’s “atrocities committed against the progeny of the Messenger of Allah.” On finishing his address, he wept bitterly and told his kinsmen, the Umayyads, that he was not prepared to carry the burden of their sins on his back. Therefore, he said: “Do as you wish. Load this Caliphate on whomever you please. As for me, I am out of here.” This all has been narrated fully in Taariikhul Khamiis, Volume Two, page 301.
There you are! Having read all this (despite leaving out much more) would you still think of Yazid as Amirul Mu’minin? Would you still do so when his own son did not consider him to be qualified to have this title? Who would know him better, his son or an outsider? I leave this to the readers to decide.