All of the above make sense. But I'll have to say I find it hard to see Ennis as this macho man who feels threatened by whether his wife is impregnated or not.
In the scene where he says he'd be happy to leave her alone if she doesn't want no more of his kids, I read it as, "Thank god! Here's an excuse to get out of this." And in the conversation with Jack about sons vs. daughters, well, that's story vs. movie, but still I don't see that as necessarily a sign of machismo (I used to want a girl for a kid -- maybe because I am a girl -- but just got little boys, yet I'm really not THAT much of a girly-girl, and by the time they were born I was perfectly fine with it). In the Thanksgiving fiasco, I don't see Ennis as being castrated so much as going along just to be nice to his kids (not to be the "sad dad"). I see no sign that he is bothered by either his inability to support his family or Alma being impregnated by another man. He could have done either if he'd wanted to (taken the job at the electric company, had sex with Alma), but it appeared to me he didn't want to.
Here I am, as usual, dilligently defending Ennis. But really, that's really just how I see the movie!