The phrase bad guys has been used incessantly by the media––and by ordinary speakers influenced by media language––as a handy substitute for enemy or terrorist in referring to the Iraq and Afghanistan wars. This can perhaps be understood as a convenient covering reference to an enemy that does not belong to traditional warfare. They wreak evil and are “bad,” but they are often not soldiers in the conventional sense, since they may not belong to a conventional army.
But the use of this phrase is semantically fraught with the wrong connotations, for the following reasons. First, guy is a colloquialism that is associated with an informal attitude to the referent that is, moreover, at least stylistically neutral if not entirely hypocoristic in contemporary English. Second, and more tellingly, the phrase derives from the world of Hollywood motion pictures, where evildoers of all sorts have always been referred to as “bad guys” in opposition to “good guys” in denominating the characterological identity of the dramatis personae of movie (and, by extension, television, etc.) plots.
There is thus a strong current of trivialization whenever the enemy and terrorists are referred to by this phrase. This colloquialization has the unintended effect of minimizing the evil wrought by them, just as it is by its frequent equivalent bad actors. Both must be expunged from public discourse because any reference to the enemy or to terrorists that even subcutaneously allows for a quasi-endearing evaluation of their status can result in a weakening of the resolve to defeat them. It is thus a failure of thought that cannot be tolerated for moral as well as rhetorical reasons.