from WIKI:Every non Muslim who knows a bit about Islamic history feels the same.how can you support people who killed Muhammad's daughter,son in law and grandsons and call himself follower of Muhammad.
Umar ibn Sa'ad ordered a man to dismount and to finish the job. Khowali ibn Yazid al-Asbahiy preceded the man but became afraid and did not do it. Then Shimr ibn Dhiljawshan dismounted his horse and cut Hussein's throat with his sword whilst Hussein was prostrating to God. Just before his throat was about to be cut, Hussein asked Shimr ibn Dhiljawshan, "Have you done your prayers today?" and this shocked Shimr because he did not expect anyone in the position of Hussein to ask such a question. Then Imam Hussain (A.S) asked for the permission to do Asr prayers (because it was the time of 3rd prayer). Shimir gave the permission to say the prayers and Imam Hussain (A.S) started prayer and when he went into Sajda. Shimr ibn Dhiljawshan betrayed and said: "I swear by God that I am cutting your head while I know that you are grandson of the messenger of Allah and the best of the people by father and mother" he cut head of Hussein ibn Ali with his sword and raised the head .[63] Then ibn Sa'ad's men looted all the valuables from Hussein's body.
and they still have guts to call themselves Muslims !