Bilbo´s treachery

[Lalaith]

Feeling the need to check the canon in the aftermath of the DoS nonsense, I have gone back to the Hobbit for the first time for, I have to admit, decades. Re-reading it reminded me of what has always troubled me, ever since I first read the book as a little girl.
Bilbo offering the Arkenstone to Bard and Thranduil was just plain wrong. Thorin´s rage always felt to me entirely justified. Bard had a very tenuous claim to some of the Erebor treasure. Thranduil, none whatsoever. It was nothing but scavenging. Quite why Bilbo felt the need to toad-eat the opposition and betray his brothers-in-arms I just don´t understand.
And not satisfied with selling his quest companions down the river, Bilbo, during the Battle of the Five Armies, "preferred on the whole to defend the Elven King". What exactly has Thranduil done to deserve this loyalty? And then Bilbo randomly gives Thranduil a necklace of silver and pearls given by Dain? This fawning over elves and ingratitude to dwarves puts Bilbo in a very poor light.