The Hobbit: Why Do Thranduil And Bard Still Respect Thorin Despite His Dragon-Sickness Cruelty?

gamerant.com:

At the start of Bilbo’s journey to the Misty Mountains, Gandalf warns the hobbit that he cannot promise that Bilbo will return to The Shire alive by the end and that if he does, he will not be the same as he was. This couldn’t prove to be more true, as Bilbo survives some of the most harrowing experiences of any of the characters in either The Hobbit or the Lord of the Rings. Along the adventure, Bilbo is nearly roasted alive by trolls, nearly squashed to death by battling stone giants, nearly skewered by goblins, nearly eaten by Gollum, and nearly killed in the myriad of battles that he faces for survival.

But arguably one of the most difficult experiences that he faces in that long year is watching Thorin, a friend whom he greatly admires and cares for, succumb to dragon-sickness. Bilbo experiences, more than any of the others in the company, the way that Thorin slowly starts to lose his mind to greed and gold-lust. And the more paranoid Thorin gets, the crueler he becomes to those around him, his own kin, and the ones that they have promised to help. That is when the famous line “I will not part with a single coin. Not one” comes in, and Bilbo realizes that unless he does something, it will be too late for Thorin to ever come back from the brink.

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So Bilbo takes the Arkenstone and offers it to Bard of Laketown, and Thranduil of Mirkwood. And both of these characters hold no love for Thorin, if anything both of them despise him, because he has denied them something that is honorably theirs. For Thranduil, it is the White Gems of Lasgalen, the precious necklace that he made for his wife before she died, a reminder of his love for her and a very sentimental keepsake