Why is their reputation relevant? They're dead.
Reputation guides your behavior toward that person. But they're no longer around. There is no behavior toward them. They're gone. Their reputation is no longer relevant.
> Reputation guides your behavior toward that person. But they're no longer around. There is no behavior toward them. They're gone. Their reputation is no longer relevant.
It also culturally informs someone's perceived suitability as a role model. It doesn't matter to the dead person if they are held in high or low esteem, but it may matter to people in their formative stages deciding whose influence they follow and whose they shun.
I'm not saying it's right to not "speak ill of the dead". Just that that's the reasoning I've seen in my family.
Speaking only positively about people distorts the reality.