When talking about morality it is difficult to distinguish between different peoples view points. How some people view what is right and what is wrong could easily be completely different from how others view the same thing. Different religions value life more than others do. Both sides of this argument ultimately do have their good points but ultimately what it comes down to is asking if it is morally alright. Think about this for a second, if a killer kept you hostage for years and tortured you none stop and you finally were freed because he died, would you cry from happiness. This is in some sort of way celebrating the death of the killer, maybe not to the extend of screaming in the streets, but in some way it is your own celebration. Maybe the amount of celebration that should be put into the death can get morally wrong. That brings about the question, how much celebration of a persons death is allowed to be had before it becomes morally wrong.
The celebration of their death is a celebration to an end of the actions which made them so hated to begin with. It is perfectly natural to feel relief and elation at the end of a terrible era which is precisely what the death of OBL was viewed to be.
Celebrating the death of another human being disgusts me. To me, it is a tragedy. Whether purely tragedy, or tragic necessity. Even a death that was well-deserved still pains me, because I think of the wasted potential of that life. I think of the fact that even the worst of us are still human beings. The end of a life is a somber thing. In the case of an evil person, it can also be a cautionary tale. Learn from everything, and everyone, so that you will not make the same mistakes.
It seems to me that celebrating death is rather barbaric. Even in victory, or in payback, death is something sad. When I think about Hitler and Osama, and those who have done terrible things in the past, in my mind, their life was a tragedy. Even if I want people like that punished and eliminated from this world, I also can't help but acknowledge that they were once a baby, held in their mothers arms. I'm aware of the crimes they committed, but I cannot cheer to see them killed, I can only really be relieved that the tragedy is over. I know it's a classic thing, to be glad upon a victory, to slay your foe, all of that. But to me, there's something somber about the fact that it ever had to come to this. I know some death is heavily deserved, but it should never be celebrated.