Are terrorists justified in killing us if we say anything to make fun of Islam?

Naturally no... However the issue is much bigger than that, with a larger context, that must be understood to make sense of what is going on. Islam allows for critique, questioning and commentary in Islam. However it does not allow for insults, abuse or other uncivilised behavior and for those who insult or abuse God or his prophet it is seen as a capital offense. The point that often gets missed is that it is only the state can exercise force, with due judicial processes in place. Individuals are not permitted to utilise force or violence. Thus, viewed in this context Islam's take is little different to those of most modern states. Worse, modern states like the US recently ordered the assassination of one of its citizens in Yemen, Anwar Awlaki. Why? Criticism of US foreign policy... The issue really comes down to one of insulting those values people deem important. It naturally elicits an emotive reaction - consider the Wootton Bassett case in the UK in 2010 when some Muslims wanted to do a peaceful demonstrate against British troops coming back from Iraq, the UK was in uproar with emotive headlines... Issues like these are important to people and emotionalism results when they are touched.