The ethics of participating economically in blood diamonds is one thing - the other side of it is millions of couples who have been socially pressured for generations into putting good money into a massively depreciating asset. I hope that declines.

Not sure where you live, but that social pressure was/is very soft in Europe. Absolutely nothing happens if there is no diamond, its just people self-pressing themselves in some variant of childhood-like mentality and competitiveness. In my family line, nobody ever bought anything like that.

For any man, for past few decades (at least 3-4) a woman insisting at all costs on big shiny natural diamond is a massive red flag for undesirable personality traits. Given stable divorce rates and general misery on all sides before and after that red flags are and should be considered very intensively. Once physical attraction wanes, only personalities remain.