We don't say RadiyAllahu 'anh to Yazid. We believe that Yazid was a Muslim, but he was fasiq. There are many Sunni narrations which say that Yazid drank alcohol. But at the same time, we also believe that Yazid was NOT the one who killed Imam Husayn RA in Karbala. The one who killed Imam Husayn RA was a Kharijite. And when Yazid heard the news that Imam Husayn RA was murdered, Yazid got shocked and cried. Wallahu a'lam. Anyway, why do the Shiites love to mourn the death of Imam Husayn RA? You should actually be happy! Because the tragedy of Karbala indicates that Imam Husayn RA was shahid and he is placed in heaven as the leader of youth! If you mourn the death of Imam Husayn RA out of loving him, why don't you mourn the death of Rasulullah SAW too? Why don't you mourn the death of Imam Ali KWH too? Please answer that, I am very confused with you Shiites.