Read KHILAFAT O MULUKIAT by Maudoodi to find out what he wrote about Muawiyya, r.a., and Yazeed. In fact I don't agree with much of what he wrote . It was too harsh.
Here are a few facts which Qaseem and his shia friends cannot counter:
1.Yazeed did NOT kill Hussain.r.a.
2. Yazeed did NOT order the killing of Hussain. r.a.
3. Yazeed was very protective and gracious towards Zayn al-Abedin, r.a., and other survivors of Kerbala.
Was Yazeed a Muslim?
Of course he was not comparable to Abu Bakr, Umar, Usman and Ali, may Allah bless them, nor to his father.
However some of the greatest Islamic scholars have debunked the claims that Yazeed was not a Muslim or that he was corrupt.
Among these scholars were Imam Ghazzali and Ibn Khaldun.
The brother of Hussain, r.a., testified that Yazeed was not corrupt in his personal life.
Remember that Hussain, r.a., did Bayat of Muawiyya, r.a., and in all that time, Muawiyya's son did not trouble him in any way.
I don't like Yazeed but as a Muslim I don't have the right to fabricate stories against one whom I don't like.
Most importantly, authentic hadith have reported that Yazeed was present in the Jihad army of Islam which advanced on Constantinople.
Kaukab Siddique, PhD