Some random thoughts:
-Elrond cautioned the Fellowship against taking oaths.
-Considering your example of "The Paths of the dead (definitely not a great
thing, as the warriors promised things that they could not fulfill)" I
would say that it was the breaking of the hillmen's oath to Isildur that was
wrong, and not the oath itself. And yet, in the end, it was fortunate
they broke their word, or Aragorn would have no one to call on for aid.
-Doesn't Gandalf explicitly say that Pippin's oath to Denethor was a good
thing?
-I don't think you mentioned the oaths of Cirion and Eorl, intended to be
binding on their heirs. Certainly it's a good thing that Rohan came to
Gondor's aid. And Aragorn and Eomer renewed these oaths of friendship
after the war.
-What about the oath of Beren to Thingol, swearing that when they meet again
he'll have a Silmaril in his hand? Happy and sad consequences to that
one.
