LotR -- Book 3 - Chapter 01 - The Departure of Boromir

[Raynor]

Originally Posted by Neithan Tol Turambar

Boromir was bound by his duty to Gondor and the Steward to slay Aragorn by any means necessary, and the others of the company should they present a threat.

Who made explicit such an obligation to kill, what sort of threat would justify that and when did such a threat become apparent in FotR?

Originally Posted by Neithan Tol Turambar

His duty to protect Gondor was the single greatest purpose and mandate in his life. He was born just so that he could perform this duty.

That's is quite a statement. Can you back it somehow? In the Athrabeth, what Eru requires of His Children is belief in Him and Estel, not some 'blind' allegiance to a narrow political concept such as a city.

Originally Posted by Neithan Tol Turambar

Therefore he was bound to get the ring and use it to the last defense, and, possible, the defeat of Sauron.

His very own words ("a madness took me, but it has passed") show that he acted out on the corruption of the ring, outside his 'duty'. If he felt he did the right thing, he would not have felt such a remorse, and cry for his curse.