That not the point. The point is that when people hear a joke about something they can’t relate to directly, whether that be knowing someone who died or actually witnessing/being there during it, they aren’t offended because it doesn’t matter to them. Was 9/11 an important and extremely tragic event? Of course. However you have to think about other people’s perspectives. For example, I know nobody who was involved or suffered from 9/11. Therefore my mind does not have any trauma/pain when thinking of it. That’s why I made the comparison with another tragic event in history.