Hmm, I would disagree that Thorin's quest was "really" motivated by greed. The Dwarves' gold is not just gold to them; all their riches are also their creations, their achievements. Seeking and delving for more is not so much their greed, but their calling. The Elves of Lorien were grieved to leave their forest behind - their beautiful forest, with unique mallorn trees that they took care of and "customized" to fit their character and their needs. Is it the Dwarves' fault that the mallorns of
their character are jewels and gold?
Furthermore, getting some gold on the side is seen mostly as a positive thing by most people, but not of these people necessarily thirst for that gold for the sake of the gold. Plus, Thorin's people were dwindling away in the unpromising mountains in the west. Wanting to return their former gold -
their former self-esteem, character, and status in society - does not equate to greed.
Thorin was taken by greed towards the end of their quest, but I do not believe that greed was the hidden true motivation. They really did have a home and a status to retake. And Thorin wanted revenge too. Yes, Thorin's greed was the main cause for the disputes between the Men, Elves, and Dwarves, but the Orcs would have come either way, so the battle would not have been prevented. The only thing I can see happening if Thorin was more generous is that when the Orcs attacked, he would call for help, and everybody would send him legions half the size of those they brought to get their share of the gold - if at all - and the battle would be lost. So in a roundabut way, Thorin's greed actually allowed for enough strength to come together to defeat the Orcs, which does not do Thorin much credit but is a funny plot twist.
As for the Arkenstone, well, everybody decided to let go of
their greed and recognize the others' right to some things (that spurred the others' greed, but that's water under the bridge). Yes, the treasure must be shared. But Thorin also deserved the respect. I think he truly wanted the Arkenstone. Sure, that desire was increased tenfold to almost insanity by greed, but he did not only value the Arkenstone for its monetary value. The Arkenstone was his personal Erebor. When Thorin's death put a little damper on things, and he was the first to recognize his wrong, others began to recognize theirs as well - and the portion of right in other people's wrongs. Had Thorin lived, I do not believe that it would be that simple and that clean; but he had not, so this is how it was.
Anyways, really cool thread - I would post an actual analysis of a different character, but I have very little time, and this post took up a lot already. It's a very interesting topic, I will definitely come back to it one day when I'm not as busy.