it is due to their share ignorance ........
they need to consult sahih bukhari and sahih muslim ......who have not mentioned nething negative about hazrat yazid.
in jung jamal sahaba fought against each other but we dont consider them impious.
Yazid is responsible for what happened in Karbala. It was his government and his troops who committed those attrocities. Supports a criminal = supporting his crime. You need to install some fear of God in your heart.