It was a cowardly act because the victims were innocent civilians who had no warning and, had they been warned, no means of defending themselves.
Physical bravery and a willingness to die are not the issues here. Certainly it took guts to sit in those cockpits and watch the buildings rushing toward them.
No, the cowardice I speak of is the moral cowardice of the sneak atack on innocent men, women and children (there was a day care center in the WTC). The Pentagon is a legitimate military target as are the White House and Airforce One. A surprise attack on them could be construed as having some justification.
But the attack on the Twin Towers was an act of cowardice.

troll