No word is so misused as the word “cowardly.” Terrorist attacks are often said to be cowardly, when in fact the terrorists who carry them out for the worst of ends are sometimes extremely brave. They risk their lives and even intentionally lose them by their acts. At the very least they risk long and condign legal punishment and public opprobrium. I doubt if one person in a thousand can claim to have acted in his life as courageously as most terrorists.
The reason we call terrorists cowardly is that bravery is generally considered a virtue, and we are reluctant to accord people whom we abhor any virtues at all. We want our enemies to be endowed only with detestable qualities, and we are only too aware that courage is the virtue without which other virtues cannot be exercised. If someone were to say “these brave terrorist attacks,” we should suspect him of sympathizing with them.