The point is not that it's a bad thing that he's dead - it's not a bad thing at all, imo. The point is that it is a bad thing to be seen as a people who revel in the death of their enemy. It legitimises the actions of Bin Laden, as he did exactly the same thing, and the rest of AQ (or whoever) do too. You legitimise the actions of terrorists everywhere.
The short-sightedness of the celebration over killing a single man is, frankly, astonishing. These people are criminals, and should be treated as such - treat them as combatants and you legitimise them as equals; give them a fair trial and you show not only that they are criminals, but that you are better than to stoop to their level.
Yes, it's about winning, but you have to define what winning is. It's not the death of one man, no matter how hated. It's not the killing of Taliban leaders with drones (legally questionable, too). It's proving that this way of life with justice and the rule of law is better. It's an ideological battle, and it's one that crowing over the death of an enemy, or his deliberate targeting for death, doesn't help to win - quite the opposite, as it turns us into hypocrites. And ultimately, you can't kill the real enemy with bullets, because the real enemy is not a person, it's an idea.