I had a thought today (I know, SHOCKING).
There are a lot of people who, let's say, don't really buy the premise of the LS. They are upset by Ennis moving on, feel that Jack isn't being honored, yadda yadda.
Let's think for a moment about how these same people might view the story if it were not fanfic. If there was no Brokeback canon, and they were reading about a guy named Ennis who we knew had lost his lover and was still wallowing until he met someone new.
Do you still think that anyone would be against Ennis's new romance? No. They'd be saying "Ennis, you need to get OVER that other guy...what's his name, Jack? It's been years. It's time to move on!"
My point is that the story on its face, disregarding the backstory, is one in which most readers would root for the protagonist to get on with his life and let go of his dead lover's memory. It is only the sometimes feverish attachment to Jack that puts a different spin on people's perceptions.