Thorin is kind of a mess, isn't he? And it's hard to make sense of him in the book as we don't know very much about him before now, but what I tend to think is he's got an ideal of kingship that he's never had a model for, and a lot of experience of failure and ruin, and a very strong sense that the world is not the way it ought to be but no clear idea of how to put it back together again, which is why he fails so miserably when actually faced with a kingship decision, ie, Bard demanding a (perfectly justified) share in the treasure.

(I see why they put Thorin's more personal hatred for Elves in general and Thranduil in particular into the movie, but I do think it simplifies things in a way that makes them less interesting.)