These posts put that idea in mind. I too have been bothered by James' partiality for the uncouth Thorpes. It seemed so foolish, and troubling esp. since he's headed to be clergy as pointed out nicely by BarbaraB. (James is worse than the Edward Bertram in this!)

Perhaps a literary purpose is to show that, even when her own older brother goes against her, Catherine will do what she believes right. She's young, inexperienced, and immature, but she has a good head on her shoulders and wants to do the right thing in every case. She holds a lot of promise & these things make me like her more, and want to know how things turn out. Trying to imagine what in the world could James be thinking was troubling me.