Pointing out that diamonds specifically are not actually special, unique or rare gems and that marriage oaths they are intended to represent are still likely to be broken, does not make you as smart as you seem to think you are. All of this is already well-known and well-accepted by the vast majority of the population. Swearing on a Bible or just verbally affirming that you promise to tell the truth in court, again, entirely symbolic. However, these are the customs that the general population has chosen to acknowledge, and it is the ritual, the recognition of widely-accepted customs and traditions, that makes them valuable as signifiers that one is, to some degree, participating as a normal member of society. Like putting up a Christmas tree or singing the national anthem at a sporting event. Opting out is absolutely fine, but it's not a sign of enlightenment.
Subordinating women and minorities/outsiders “are the customs that the general population has chosen to acknowledge” for most of civilized history “that ma[de] them valuable as signifiers that one is, to some degree, participating as a normal member of society”. I would encourage you to never use that as an argument for anything, ever. It is devoid of weight or reason. You can do better, I promise.
The problem you're having is that you're unable to view purchasing a diamond in non-economic terms. It isn't "absurd" or "non-advanced," nor are people "duped" into making "supremely poor financial decisions." People aren't as dumb as you think, they know that a rock doesn't really represent anything, but they enjoy giving and receiving diamonds, and pretending that they do symbolize a commitment, and sharing that belief with friends and family.
You think my previous comment is "devoid of reason" because it's about ritual and symbolic gestures, not about economics, concepts you either cannot comprehend or choose not to. Which is fine -- most atheists believe they are wiser than believers, for example -- but no amount of rationality or logic is going to change people's minds.
