It is kind of disturbing how often this happens in American movies. Even Aragorn killed messengers!
About killing messengers:
That's actually in Herodotu's original. The upshot of that was otoh that it angered the Gods, and to make amends two Spartan volunteers set of to the court of the Great King to offer up their lives.
The Great King, who is always depicted as supernaturally generous (worked fine for him, as he used it agressively, to assert his superiority), was impressed with their moral stature and resolve and so pardoned them, allowing them to return home.
This kind of highlights the superiority of the ancient Greek version of events. Killing messengers was an act of hubris. Messengers are outside of the conflict. When the Spartans did this, it was a crime, and the Spartans recognised that and the need to pay for it.
Of course, these Spartans were asked by other Persians why they had offered their lives like this, of their own free will. And the Spartans replied that is was exactly because they were free men, only subject to the laws of their society. This the Persians, according to Herodotus, found entirely inexplicable, as they were all "slaves" of the Great King, whose only law was the whim of their ruler. They had no concept of being free in the Greek sense (in the Greek version of things).
That's the opposition in the ancient Greek version: Freedom and law against despotism and whim. But if the despot is a good man, his subjects are virtuous and his rule good, like Cyrus. Unfortunately that kind of godlike power tends to corrupt, and lacking the laws of the Greek to rule them, the Persians would fall prey to the same weaknesses as their ruler, like Xerxes (not to mention Cambyses, who is depicted as stark raving mad).
What's so compelling about the ancient Greek version is that the story is tragedy - both sides are noble, chivalrous and corgeous, but set on the destruction of each other. Of course the Persians have a single, but fatal, flaw, and this gives the Greek victory.
Too bad Hollywood (or at least it doesn't trusts its audience to) can't grasp the idea of tragedy anymore, and make it into drama.
