Two thoughts:
1.) It is incredibly disrespectful that this group would hold an event designed to be disrespectful to Islam and inflame Muslim anger. I think Christians would be profoundly offended if a group decided to hold an event encouraging participants to depict Jesus in an offensive way - such as in sexual poses or committing gross sin. It is the antithesis of loving one's neighbor/enemy and Christians should not be involved. That is not to say that we cannot expose the error of Islam and present Jesus as God incarnate, but we cannot disqualify our words by unloving actions. According to Jesus, His followers are to be characterized by love - love for each other, love for one's neighbor, and love for one's enemies. By turning a blind eye to these events (or even supporting them!), we help to radicalize Muslims, perpetuating an extremely serious global problem. Unfortunately, to many Muslims overseas, the United States is seen as the representative for Christianity. Stories about events like this travel around the world through Islamic circles. Wouldn't it be great if Christians protested this event and THAT was also known throughout the Islamic world?
2.) The two who attacked this event are a sad example of radicalized Islam, a religion that knows nothing of separation of church/mosque and state in most parts of the world. To many involved in this religious system, the only means honoring their understanding of God is to exact justice against those who would offend their god. We certainly must resist evil, but we should also seek to built inroads into the Muslim world so that Jesus would be known there are the only begotten Son of God Who is calling all to redemption in the Kingdom of God.