This seems to be an American phenomenon. Americans--women in demanding it, and men in acquiescing to it--are keeping this commercially confected "tradition" alive through a vanity bred and reinforced by corporate greed and consumerism. It's not that a diamond ring is bad per se. It's the artificial and frankly socially destructive stipulations around them. It's almost as if the marriage and future spouse were an afterthought, secondary to the actual ring! It is utterly deranged.
Similar things can be said about lavish weddings couples can't afford and go into debt for. It's a culture of spectacle and pretense. If you're not a rich aristocrat, don't pretend to be one. You're not "temporarily embarrassed millionaires".
If you think lavish spending on weddings and engagements is an "American phenomenon," you're badly mistaken. Read up on weddings in India, Armenia, Cambodia, Afghanistan...
When diamonds held their value they were a useful vehicle for dowry (and showing off your dowry). Now that they don't...an Instagram account with 100K followers might be a suitable modern replacement
Eh, people are going to people. My wife and I are American and we did not do a diamond ring (we just exchanged simple hard wood rings).
In any case, what I really object to is your assertion that women "demand" it and men "acquiesce" to their demands. In most cases people just figure its the tradition and its fun and frankly, if I were a woman, I wouldn't say no to a costly sign of commitment if the dude wanted to do it. But most of the women I know have no deep commitment to the practice.
Even going by the nth month rule doesn't indicate that the woman _demands_ it. It is a cultural practice, no doubt one spurred on by the diamond business. But that doesn't mean every woman out there is screeching that their paramour buy them a diamond. I'd actually be willing to bet that a significant portion of women are ambivalent about the practice.
Similar things can be said about lavish weddings couples can't afford and go into debt for. It's a culture of spectacle and pretense. If you're not a rich aristocrat, don't pretend to be one. You're not "temporarily embarrassed millionaires".