Periodic reminder that "don't speak ill of the dead" is for, like, not mentioning at her funeral that Aunt Sally was a drunk and a lousy cook. It's not for suppressing public discussion of public figures and their complicated legacies.

Or, put another way, the obligation to "speak truth to power" is way more important than the obligation "not to speak ill of the dead". One is about justice and the other is about politeness. To be frank, FUCK politeness.