Stoic,
A surprise attack upon unarmed and unsuspecting civilians is always a cowardly act. Is there another rational way to see it?
Do you really suggest "a heroic self sacrifice of courageous conviction" describes a suicidal terrorist attack?
You assume that religious beliefs are the motivation of each cowardly terrorist act and that facing a painless and instantaneous death requires strength or courage.
While religious belief may drive a few of these people, it is more accurately described as delusional fanatacism.
For the others, I suggest misguided anger and hate, the manipulation of weak minds and spirits, and the disillusioned, lost and ready to die make up the rest. (As well as some who do it to buy money for family and obviously don't hold much value for their own life or those nameless and faceless innocents they target.)
It took a certain level of "guts" for the terrorist animals who did 9/11, but don't confuse that with the fact that attacking an unarmed, unsuspecting, and innocent plane load of passengers and crew was anything less than cowardly. Don't even suggest that the orchestration of their own painless deaths while trying to kill as many innocent people as they could was anything less than cowardly.