I shouldn't have to preamble this, but it's a touchy issue, so I will. I don't agree or identify with the aims of the people I'll be talking about. Their methods are objectionable and repulsive. Frankly, I think they represent some of the least redeeming characteristics of our species, and they're motivated by some of its most backward, primitive attitudes.
But they're not cowards.
A coward is someone too paralyzed by fear to act. Clearly, that is not case here. On the contrary; these are people so motivated by apprehension, and anger, and hatred, that their need to act overwhelms their otherwise ordinary senses of justice, compassion, and reason. Their philosophy empowers them with the belief that if they are condemned by all their fellow creatures, that's nothing, because they will reap the praise and reward of the only being whose opinion matters.
I think we do a real disservice all around in simply throwing out the word "cowardly" to describe incidents like the hotel attack in Kabul. It mischaracterizes the motivations of the attackers and makes it less likely we'll be able to understand, and thus effectively counter, their methods. As I see it, these are people who feel themselves, their culture, and their religion (their god, if you will) as under attack by forces too wealthy and powerful to take on directly. Only indirectly can they attack us, by ducking under our formidable armour and striking us where we're soft and unprotected. Lest the temptation to reaffirm this as "cowardly" be succumbed to here, I would also remark that much of the Second World War was fought on a similar basis. When the prospect of being utterly pulverized by attempting to wage direct warfare across the English Channel stalemated the land war for four years, neither the Germans nor the Allies had any compunctions against targeting and killing civilians on the other side, from the air, and by the hundreds of thousands, and eventually millions. What feeble defence could be offered by fighters on either side to wave after waves of bombers was little more in comparison than what suicide bombers or gunmen face in armed guards. The bottom line is, I don't see how we can call people who risk their lives attacking essentially defenceless people "cowards" if we're not prepared to say the same of men who risked their lives to roast alive, from above, civilian men, women, and children indiscriminately in their hundreds of thousands in Dresden, Tokyo, Hiroshima, and Nagasaki. And I don't think we are.
I think we do better to stand up before the world and tell them these attacks are "pointless". These men give up their lives, beggar their families of their love and support, and sicken mankind with their poorly-considered bestiality to achieve nothing. Nothing changes that they could remotely consider advancing their cause or addressing their aims. All that happens is an increase in human misery for their own families and those of their victims, and a momentary release of schadenfreude in like-minded people that quickly fades. If anything, their goals are made more remote as these tactics tend to stiffen the resolve of their opponents and make them less willing to see things from their point of view or try to compromise.
So the word we should use is pointless. And we should make it clear why.