Keep in mind that not everybody lives .5 mile away from Ground Zero.
The problem here is that, while everyone knows on some sort of indistinct, intellectual, level what happened, if we refuse to look at the footage we deny ourselves the truth of what happened.
In many criminal cases, including murders and rapes, there are pictures of what the victim went through. A good prosecutor knows to show those pictures to the jury, even though it would be tough on the victim or victim's family.
Why?
Because even though the jury has heard what happened, it doesn't hit home how heinous the crime was until they SEE what happened.
The "jury," in this case the American people, may have "heard" what happened, but they are starting to forget. They need to see it again. Otherwise, and we are seeing it happen already, they start to forget the true horror and return to complacency (for example, look at the way people want to call this a tragedy. It was not a tragedy. That implies some sort of accident. THIS WAS MASS MURDER).
The footage must be shown. Not for the victims. Not for the neighbors. But for the nation. We cannot allow the media to shield us from the true horror and, in doing so, shield us from the resolve we need.