Seeing as Thorson is the only non good member of the party he may make some unpopular choices, again, I'm looking forward to seeing how it plays out.
Not sure I'd describe Thorson as arrogant, but I would definitely agree that in this he is very self centered. Everything has been sharpened to an absolute monomania, he has spent the last three months doing little except looking for Lamm, working to stay in the city, and fantasizing about how to kill Lamm. Don't expect him to suddenly change...
We'll see what happens, I have a definite plan in mind for Thorson's character development and a clear concept of his morality, loyalty, and style of relationships. He's not mindless, and priorities can change over time...