The consensus seems to be that "cowardly" is used as victims of terrorist attacks may not return fire. Thus eligible attack is only against equally equipped opponent. It seems that politicians accuse the terrorists of not adhering to medieval theoretical chivalric code. Unfortunately this is not the case, if so then:
- snipers
- drone operators
- any air attack on a target without appropriate AA defence
- pilots of F22 Raptor
- submariners
- pilots using surface-to-air missiles (not many countries are able to shoot down
missiles). are all cowards. Of course it is not the case.
Using the word coward is in fact purely political. It also sells well in media. Moreover this also contains the message "this is not the pattern one should reproduce". They can't use the word "dishonest" as this is no longer shocking (even in the Bible David killed Goliath, also Judith cut off the head of the Holophernes at night). In fact in military terms being "honest" is an anomaly.
Personally i think that if the word "barbaric" or "uncivilized" would be better. Using "cowardly" is just best from the political point of view, as this feature of character is disdained by almost everyone.