Burying the Dead

Why, may I ask, is it necessary to praise the dead? I know the cliche of not speaking ill of them. I'm aware that it's frightfully bad manners. However, the requirement that we speak only well of those who have passed away results in grotesque mythologies being built up around mediocrities and villains. William F. Buckley opposed the Civil Rights Movement, thought poor people should lose the right to vote, and wanted to purge the academy of liberals. Why must I remain silent while others prattle on about what a wonderful person he was? A person who smiles while murdering another remains a murderer, however charming that smile may be.