A few thoughts from when I heard last night that U.S. soldiers killed Osama bin Laden.
This passage of the Tao Te Ching resonated most with me:

Weapons are the tools of violence;
all decent men detest them.

Weapons are the tools of fear;
a decent man will avoid them
except in the direst necessity
and, if compelled, will use them
only with the utmost restraint.
Peace is his highest value.
If the peace has been shattered,
how can he be content?
His enemies are not demons,
but human beings like himself.
He doesn’t wish them personal harm.
Nor does he rejoice in victory.
How could he rejoice in victory
and delight in the slaughter of men?

He enters a battle gravely,
with sorrow and with great compassion,
as if he were attending a funeral.

Another translation of the same passage:

Weapons are terrible things.
If you want to get right with Tao,
reject weapons.

The Master,
knowing all things came from Tao,
recognizes what he has in common
with his enemies
and always tries to avoid conflict.

But when there is no other choice,
he uses force reluctantly.
He does so with great restraint,
and never celebrates a victory;
to do so would be to rejoice in killing.
A person who would rejoice in killing
has completely lost touch with Tao.

When you win a war,
you preside over a funeral.
Pay your respects to the dead.

Next, the images of people celebrating at the White House, Times Square, Ground Zero, and so on reminded me, as I’ve read it reminded many, of the scenes of people celebrating after the towers fell on September 11, 2001.
These scenes reminded me of the Godfather movies — one group kills people in another group, the others in that group feel compelled to kill in revenge, no one can remember how it started, no killing ends the cycle. Each group is convinced either of its righteousness or that it is following rules that justify its actions. Cicero said “the law is silent during war” and this killing seems like the lawless killings of those movies.
No matter how right or justified anyone feels about killing Osama bin Laden, we can rest assured, as far as these emotions are concerned, he and his collaborators felt just as right and justified, with evidence that was, to him, equally compelling.
I don’t know the details of if bin Laden could have been captured and tried, but I feel that outcome, if possible, would have reduced future violence more, even if at the expense of the satisfaction of those who want him dead. Obviously this feeling is just a feeling — I can’t predict hypothetical futures better than anyone else.
I hope people feel safer. I hope they are safer, but there is no way to measure what happens against what could have happened in a hypothetical other future.