Let's see, these "non-cowards" attacked civilians on a civilian aircraft (cutting the throats of unarmed female cabin attendands, as is suggested by the report that an attendant's hands were found bound together) with the near-certainty that they would not encounter any armed adversaries on board.
Then they flew their planes into buildings at 400-500 miles per hour ensuring themselves of a quick, painless death followed by -- so they were all convinced -- instant transference to paradise where they were greeted by nubile virgins.
Maher and you are wrong. The typical WWII, Korea or Vietnam US Army infantryman (not a medal winner) showed far more courage every time he advanced on an armed enemy or whenever he stayed in his foxhole as the armed enemy approached his position.
Using Maher and your criteria, classic American mass murderers who put a bullet in their own heads after they kill their unarmed victims are also "not cowards."
Maher's firing was totally justified. His comments were as stupid as they were offensive.