I think it's completely reasonable for people to be celebrating. However, I don't see it as a celebration of a persons death as much as a celebration of relief. Bin Laden, had become a representation of fear and uncertainty so his death meant more than 'a bad man died'.
Think of it this way, a serial killer goes from house to house murdering people in broad daylight. Upon finishing his spree, he make a video to tell the world what he's done and when you call the police to arrest him, he disappears leaving a giant broken community sad and frustrated that he did so much damage without answering for it. The resentment from tragedy with no closer does not go away. If he's caught/killed 20 years later, damn right people are going to celebrate.
Also, I'm pretty sure people celebrated when Hitler died and no one judged them for it.
Think of it this way, a serial killer goes from house to house murdering people in broad daylight. Upon finishing his spree, he make a video to tell the world what he's done and when you call the police to arrest him, he disappears leaving a giant broken community sad and frustrated that he did so much damage without answering for it. The resentment from tragedy with no closer does not go away. If he's caught/killed 20 years later, damn right people are going to celebrate.
Also, I'm pretty sure people celebrated when Hitler died and no one judged them for it.