That's horrible. How could they kill innocent people, not soldiers, not politics, but innocent citizens who just wanted to celebrate a New Year's eve in a nightclub? I can't get it. Isn't any war about killing the army of your enemy and not the civilians?
NO.
There are countless historical examples of an enemy displaying ruthless terror, as a technique in demoralizing the foe. This does mean such a thing as slaughtering an entire village, men women and children.
The curious thing about the Islam religion is that somehow these fanatics generatlize "war" to "society at large" or perhaps "someplace that is sort of Westernized" or "something I don't understand" and all that translates into "Fuck it I'm just going to go blow myself up."
I believe it is very dangerous to believe the supporters of Islam who say "Oh, THAT'S not Islam" or who say "All the Muslims I know are friendly happy people" and all that other propaganda.