Is it permissible to mention the injustice of Al-Hajjaj, Al-Ma'mun, and others in gatherings and pulpits, given the Hadith: "Mention the good qualities of your dead and refrain from mentioning their bad ones"?

The mentioned hadith is weak, and the hadith "Do not curse the dead, for they have gone on to what they have sent forth" narrated by Al-Bukhari suffices. This hadith specifically excludes the openly immoral person who publicizes his immorality and the innovator who calls to his innovation. Such individuals may be mentioned with their evil for an overriding benefit, such as mentioning Al-Hajjaj and Al-Ma'mun for warning. Scholars have explicitly stated the permissibility of speaking ill of the dead when it serves a benefit, criticizing flawed narrators whether alive or dead, and mentioning the evils of disbelievers and transgressors as a warning. However, if there is no benefit in mentioning the deceased's faults, then it is better to refrain, and one should instead occupy himself with his own shortcomings.