Killing one man doesn't make the world any safer.
Having said that, I also have to say, that I don't understand why people gather in the streets, celebrating. What on earth is that!?! Where I come from, celebrating another mans death is referred to as hulliganism. We call ourselves 'civilized'. That behaviour is not an act of a civilized person.
I would have prefered to see this man brought to justice ... Killing him will make him a martyr .... which is why we probably will not be able to take a nail-clipper onto a plane again in the nearest future. ......
But Hey! This is just my personal opinion.