Should Americans Fly the flag on 9/11?

I really hadn't given much thought to this before it was asked in class. I guess that if you want to fly a flag on 9/11, then that's your decision and it's a free country, so do what you want to do. However, it seems a little weird to me to be flying an American flag on a day where over 2,000 people died in a terrorist attack. I don't think that there should be any laws for or against this policy, although I don't think that I would fly a flag on that day.