Who Really Killed the Witch King in ROTK??

[Gordis]

Originally Posted by Alcuin

or else the portion that says “when the Dúnedain were young” would mean that the manufacture of the blades was very early in the history of Arnor, before the days of Angmar, I would imagine.

I don't think so. Why would the Northern Dunedain start making anti-wraith (much less anti-WK) weapons before there was any wraith nearby?
As for "young", please compare it to this quote:

They heard of the Great Barrows, and the green mounds, and the stone-rings upon the hills and in the hollows among the hills. Sheep were bleating in flocks. Green walls and white walls rose. There were fortresses on the heights. Kings of little kingdoms fought together, and the young Sun shone like fire on the red metal of their new and greedy swords. There was victory and defeat; and towers fell, fortresses were burned, and flames went up into the sky. Gold was piled on the biers of dead kings and queens; and mounds covered them, and the stone doors were shut; and the grass grew over all. Sheep walked for a while biting the grass, but soon the hills were empty again. A shadow came out of dark places far away, and the bones were stirred in the mounds.

"Young Sun, new and greedy swords" referred to the period after the division of Arnor when Cardolan fought with its sister Kingdoms and with Angmar. "The towers fell", I believe, refers to 1409. Right after that "dead kings and queens" were buried. "Sheep walked for a while biting the grass" refers to period 1409-1636. "Bones were stirred" - the wights were sent to the barrows after the Plague of 1636.

Originally Posted by Alcuin

The phrase “when the Dúnedain were young” seems to me to refer generally to the days in which the North Kingdom still existed; and by inference, once it “died,” the Dúnedain (at least in the North) became “old,” perhaps in some ways comparable to their essential allies, the Elves, without whom they could not have survived.

I agree.

Originally Posted by jammi568

Maybe because it was so far gone and degenerated to the point that nothing would ever get rid of the stains it had recieved. Plus, there's the fact that a bad reputation is a very hard thing to get rid of, even if the things that caused it have gone forever.
It's just like the haunted houses in those cheap horror movies - they could easily know it down/rebuild it, but the reputation it gained in the mean time would make it very difficult to sell.

Originally Posted by Alcuin

Minas Morgul was polluted beyond redemption,

I am not sure about the type of this pollution: was it ecological, (like the unwholesome river Morgulduin and the meadows with a tendency to grow poisonous white flowers), or cultural (bed reputation, horrible memories connected with the place), or magical - the residual evil magic that Aragorn and K were unable to overcome. Maybe there were still a lot of wraiths and ghosts haunting the place - for real, not figments of imagination?

If Morgul-blade wraiths would likely be destroyed together with the Ring, the Houseless Elves, for instance, wouldn't be affected for sure. And I have a nasty feeling that the Silent Watchers of M.Morgul and Cirith Ungol were the Houseless, trapped within stone statues...
After the Fall of Mordor, all this ghost company may have remained in the Morgul Vale.