For the public good, I'm posting this link to an excellent article about
Misunderstanding Brokeback Mountain, in which the author neatly articulates what I've been so far incapable of articulating.
His central thesis is that Jack and Ennis, in insisting that they aren't queer, are not rejecting their feelings for each other (which they consistently own and accept) but the label of "queer." They are not willing, interested or even capable of accepting everything that goes with the label of "gay" or "homosexual." They just love each other, and all they want is to continue to be the men they've always been with that included. This is impossible, so they're reduced to their intermittent fishing trips.
It's a great, thought-provoking take on the film.