That doesn't mean you should grieve with them. Talk to a loving relative or friend or counsellor if you still feel bad about this.
Holy stuff yes, this is what I've been wanting to tell everybody I talk to about this today.
If the planes crashed into the towers for some other reason (such as the pilots being drunk), people would have dropped this long ago. But NOPE, since it was caused by the terrorists we've got to drag this on and on until it becomes a goddamn holiday.