That assumes that a more expensive ring buys a stabler marriage. Actually the opposite seems to be the case:

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2501480

That paper doesn't attempt to make a causal link. It's possible that being broke during the courtship process (when the ring is purchased) is what leads to a lasting marriage. I also can't find any discussion of the cost of the ring to the cost that could have been afforded. Is there a comparable outcome from someone who could easily afford a $10k ring but instead spends $1k vs someone who can only barely afford the $1k ring in the first place?

Nothing in my comment is saying that buying an expensive ring will save a marriage.

I'm only saying that if your marriage lasts for 10 years, which about 66% of them do, it's weird to complain about the cost of a ring when there will be very many more expensive and equally bullshit things to spend or not spend on.

The divorce rate is increasing every day. One shouldn't based a decision on outdated marriage statistics from 10 years ago. Just sayin'

the divorce rate has actually been falling steadily since about 1980.

My wife-to-be and I agreed to skip 'engagement' and the money we would have paid for a ring covered the entire cost of our wedding and an all-friends garden-party.

To this day, no-one has asked my wife why she only has a [tungsten] wedding ring and no engagement ring. So that's 50c per day saved for better causes. And we have lots of good memories from the party.

Cool, if someone's prospective wife doesn't want a ring they can spend the money on whatever they want.

Here, though, GP makes it sound like his SO wants a diamond ring.

Why is everything an investment

How many starving/diamond mining children in Africa can 50c a day feed?

A US marriage is phenomenally expensive. If you want to send 50c a day to Africa, and you can't afford it, it's probably better to cut back on dressed chairs at the wedding than to tell your future wife who wants a ring that she's not going to get one.