never speak ill of the dead
It is immoral or objectionable to say malicious or defamatory things about someone who has passed away. A: "Ah, Tom was just a selfish old bigot." B: "Mary! Never speak ill of the dead!" You say we should never speak ill of the dead, but we should never forget the misdeeds of those who were once in power, either, lest history repeats itself.
Never speak ill of the dead.
Prov. You should not say bad things about dead people. Your Uncle Phil had a lot of faults, but there's no reason to talk about them now that he's gone. Never speak ill of the dead. I hate to speak ill of the dead, but Amy was a mean woman, God rest her soul.