The mouth of Sauron

[Boromir88]

your second point. in the movie I put it to you that Aragorn did not kill the MoS because of his taunts, but because the people of the West were losing Hope. the MoS was defeating them with his words. He had to be stopped. It's as simple as that. In the book Aragorn helped to do this with a look, but that just wouldn't work in this film, so he lopped his head off.~Essex

That still doesn't mean anything. Even in the unhonorable times of war we live in now, directors show they can understand that you couldn't kill a messenger (Tolkien understood this too and he fought in the first war where really it wasn't honorable any more).

Prior to WW1 wars were seen as a "Gentleman's war." With rules that each side followed because it was considered the honorable way to fight. Directors of Troy, Braveheart, Gladiator, King Arthur...etc all show they understood this concept. You can't kill a messenger.

If the MoS was using words to defeat people then Aragorn needs to use words back to send him away cowering, like Tolkien shows. Clearly stated within the books (as well as Kuru's sig), he could not be assailed. No matter how vile, low, or cruel the MoS may have stooped with his words, you can't kill a messenger. He's not there to fight, he's there to deliver terms and may not be assailed.

Let me take some common day examples. I don't know what it's like in England but in the US if someone breaks in your house you can't kill them and say it's self defense. You may only use a force equal to that of the attacker. So if a guy breaks in your house, there's no fear for your life, he has no weapon, no fear that he's there to kill you just rob you, you can't kill him and claim self-defense. Now if he had a gun and he was pointing it at you, then of course you are afraid he's going to kill you and therefor can take the proper action in defending yourself. So, it's this concept that you can only use the amount of force that is equal to that of the attacker. Even without this, still the bottomline is you can't kill a messenger.

In this case, the MoS was using word, Aragorn can use words back. I prefer the banter that went on to the three seconds of talking and "off with your head."