Why Exactly is it Bad to Speak Ill of the Dead?

[evilkumquat]

This is not meant as a snarky question, or a belligerent post, but exactly why are the dead supposed to get a "free pass" from the living?

There have been several recent notable deaths of either very evil people, or people who helped enable evil people. For each of these passings, the threads have been full of posts gloating or chastising the gloaters.

Why exactly is it bad to acknowledge that the world is a slightly better place now that some people are gone, if for nothing more than a sense of justice?

"They aren't here to defend themselves" is a weak argument, since many bad people, while living, felt no guilt in attacking the defenseless.

"It's disrespectful" also does not work. What is it about death that automatically grants one the respect that many were not willing to grant them in life because of their evil deeds?

"Think of the family?" Did the deceased think of the families of those who they were hurting? Did the deceaseds' families try and prevent the evil done by their loved ones? Didn't the deceaseds' families usually directly benefit from the actions taken by their dead relations at the expense of someone else?

"It makes us look bad." Should we really care about what "they" think of us at this point? "They" have been working so hard for so long to hurt us; what they think of us should be the least of our concerns at this point.

So please, someone, anyone, give me a good reason why I shouldn't feel pleased when evil people die. I absolutely, sincerely want an acceptable answer to this.