Any good justification for this rule you can think of?

(Also… weird that you’re not actually enforcing it? Is it a “rule” or not?)

What a stupid rule

Can we still celebrate the sudden reduction in evil secondary to his death?

The issue is that what is presented as a single rule is actually several different rules crammed into one sentence. It strings together multiple distinct ideas with commas, making it unclear where one prohibition ends and another begins. If each of those ideas is meant to stand on its own, they should be written as separate rules rather than bundled together under a single heading.

Secondly, "celebrating death" is an extremely vague concept. Many cultures celebrate death in one form or another. Hindus, for example, have traditions that celebrate the passage into the next life. Creole culture also has a long history of turning funerals into communal celebrations.

Moreover, what exactly constitutes a celebration of death? If someone feels happy that a particular person has died, they are not necessarily celebrating death itself. They are simply acknowledging that someone they disliked is gone and, in their view, that the world is objectively better off as a result.

So if I say, "I am happy that so-and-so died," that is not, in and of itself, a morally reprehensible statement. It merely expresses an individual's emotions. No one is obligated to like another person or to feel sadness when they die. Death itself is not a moral act; the act of taking a life is. In this case, the individual died naturally rather than as the result of anyone's actions.

As a result, I see no compelling reason why death itself should never be celebrated, whether the sentiment is meant to admonish the deceased or to honor them.

Maybe amend the rule to "celebrating death of actual human beings". There's one person whose death will be celebrated far and wide, for sure.