Beheading, also known as decapitation, is a form of capital punishment, which has been around seen Roman times, but had fallen virtually completely out of favor as a form of execution in modern times, to which modernity deemed this punishment as being far too brutal or too graphic, till its recent resurgent as a form of terror in the Islamic State in Iraq and in Syria. Why beheading? Obviously, once you have captured or caught an enemy combatant, or a civilian such as a journalist, and have put that person in a defenseless state, there is not an exigency to execute that person and to do so would hardly seemed humane or justified, yet the Islamic State makes this part and parcel for who and what they are. The Islamic State justification for beheading journalists or combatants is in retaliation for military strikes against their country which invariably creates carnage and civilian death. The most probable reason that beheadings are used to take the life away from these men who are often seen to be as "pawns" in this grisly game of death, is most likely the "fear factor", the fact that it makes "good" theatre, and also, very importantly, the very personal nature of the staged death itself, since the sword or axe is controlled by the perpetrator from his hand to the neck of his victim.
The beheadings committed by the Islamic State are often taped andthen distributed throughout social online media with the attendant propaganda in the somewhat forlorn hope that by so doing so, that this act will somehow preclude future air strikes from countries such as the United States. In actuality, it does nothing of the sort, except to make it almost a positive certainty, that military strikes will continue to rain down upon them, innocent civilians will be caught in the crossfire, and that the perpetrators of these horrific pre-meditated acts, will become targets of interest to America.
What the Islamic State fundamentally gets wrong, is that there is no terroristic act that they could possibly conceive or execute that will ever get Western nations, most notably the United States, to cease and desist in protecting their own or in asserting their own massive power. If the Islamic State has any moral high ground or moral suasion on their side, they effectively negate it by executing people that have done them no harm, and in a manner that only encourages scorn or hatred of their message and their position. What the Islamic State fails to recognize is that turning the ship around of a country as mighty and as powerful as the United States, is something that takes concerted effort, intelligence, and the patience of Job, and that the sword of "avenging justice" that they wield, is absolutely nothing of the sort.
Unfortunately, beheadings by the Islamic State will not be going out of style anytime soon. While the beheadings are an abject failure in regards to successfully rectifying wrongs by Western nations, they appear to be a supreme success in recruiting other Islamic disenfranchised men to their cause and are an effective tool of propaganda. Regrettably, this is another sign of the downward spiral of man's inhumanity to man, completely unnecessary, and clearly wrong. In absence of any clear dialog or diplomacy between rival nations or people, things will pretty much continue along this gruesome, bloody and God-forsaken path.