Here's what bothers me most in priority order:

1st and worst. American soldiers were killed and injured.
2nd: It was a soldier who killed and injured other soldiers. Simply defies all we expect of our men in uniform and shakes our confidence in the military.
3rd: It happened on a US Army base that we all expect to have excellent security. It shakes our own sense of security when we see what we feel is the most secure place have such an incident.
4th: It was an officer who did this. We simply expect and have a right to expect more from those who we honor and entrust with authority.
5th: And lowest priority is that he was of Muslim descent. Only because I realize how sensitive all Americans are to that right now and it lays the foundation for over reaction. And yes, it has to be investigated to the extreme so we know what happended.

I just don't want to see my country jump to conclusions and start persecution of innocent people because of their nationality or religious affiliations. To me, if that happened, it would be the greatest embarrassment to our founding fathers.