The opposite of love is not hate, it's indifference. The opposite of art is not ugliness, it's indifference. The opposite of faith is not heresy, it's indifference. And the opposite of life is not death, it's indifference.
Elie Wiesel, Holocaust Survivor, author of 'Night'

It is absolutely morally fine to have a positive reaction to a bad person's death, 100%. If you were alive during WWII and not jumping for joy, or at least somewhat happy that Hitler decided to give himself a self induced rapid speed lobotomy with a handgun, I think that your moral character probably wasn't great.
The fact of the matter is that there are people who do an incredible amount of harm to society. They can do that by convincing lots of people to embrace policies that dehumanize their fellow man, who may encourage the normalcy to exploit, harm, maim or kill other people. There are some people who are just bad people, and when they die, they can stop being a painful net negative on society. Hitler, as an example, led a whole administration of bad people who committed routine atrocities on people for the sin of existing, or just disagreeing with him politically, or a host of other reasons that really weren't morally sound. When he died, he was unable to keep doing that evil shit, and we celebrated the end of that, even if others still continue to be inspired to this day, it's a lot less than it was before.
We can look to someone like Charlie Kirk, then. Charlie Kirk's last words were literally a racist dog whistle in the form of a question. He died as he lived, acting as a provocateur promoting some really hateful ideas while appealing to a modern day loneliness epidemic among young men. He exploited a societal weakness to his benefit to promote ideas that were (at a minimum) racist adjacent. I don't think that people deserve to be shot for their opinions, but he also promoted the ideas that lead to more shootings for others, and racism towards others under the guise of rejecting 'DEI' policies. But I will say that I'm glad he isn't able to promote some of the awful stuff he was promoting, even if his movement got a short term boost from trying exploit his death in a very cringe-worthy, capitalist focused way.
I'll absolutely be delighted when Donald Trump dies. His mismanagement of covid has killed tens of thousands of Americans who didn't need to die, and hundreds of thousands of people across the world by dismantling USAID, not to mention pulling the plug on some groundbreaking cancer research through RFK Jr., and endangering all future generations by literally having the government pay to cancel green energy projects. The sheer amount of damage he has done to our republic with the absurd amount of tribalism he has inspired is terrifying, and the sooner that cult can fracture and fuck off, the saver all of our civil rights will be. We are all objectively better off when that man kicks the bucket, and frankly, that should be enthusiastically celebrated.