>“Responsibilities as a wife”—sorry, what are these supposed to be?

Figure that out and you'll get a committed partner for life. ;)

But to start, a wife is often the sole emotional support network that a man has, and in a healthy relationship his sole source of sex.

I know what it’s like to be in a long-term relationship that is effectively a marriage already, and while a good partner (looking past the gender issue with the language now) does take the effort to provide emotional support and even sex, I don’t think that it’s mature nor healthy to call such choices “responsibilities”, because responsibilities are things that people have the obligation to do regardless of their emotional and mental well-being.

If ignoring gender norms works so well, why are all the societies buying into this logic collapsing in terms of birth rates?

My own suspicion is that when both men and women participate equally in the work force, the economy adjusts so that it's impractical for just one to work.

I think equality is a good thing; it's just that we haven't learn how to structure society to not squeeze as much productivity as possible out of working-age people.

It's because all developed societies see collapses in birth rate since reproduction was a Ponzi scheme nature imposed upon us that, as the universal revealed preference, we're eager to escape given the chance. The first developed nations tend to be the most enlightened, which is why they're the most likely to challenge gender roles.