I kind of breezed over this in my earlier posts, but the more I think about it the more I realize that the day-to-day homophobia would be really hard for Ennis (and maybe even Jack) to deal with.
We are positing some kind of transformation, I guess, that would enable Ennis to agree to the plan in the first place. But it's hard to imagine him developing a thick enough skin to stand being, as Earl and Rich were, "the joke of town." I think the potential looks, whispers, laughing, harassment, physical abuse (even if it stopped short of horrific violence) or whatever would be hard for anyone to face, day after day, year after year. Let alone someone who's kind of proud and private and shy, like Ennis. Or would he having to constantly beat people up, as with the bikers?
In that respect, they'd be better off in Denver. But there they'd have an employment problem. Ennis could probably get some kind of untrained job, but he wouldn't be happy working off a ranch for very long (judging from his expression in the pavement-spreading scene). Jack, however, could work in sales, and that might be OK for him.