Raynier posted this deep down in a reply which might be lost to you if you don't read all the comments. It would be a shame to miss it. Read it, along with the reasoning where he says such criterias would be perfectly valid for his own daughter: https://news.ycombinator.com/item?id=5404423
It seems perfectly valid, yet I could not disagree more. We are forgetting a important (4) : you fund atrocious wars and dictatorships. That's a strong negative externality.
When you see a diamonds, instead of seeing a shiny rock, you should see part of a human soul instead, a fraction of a person who died in vain for this worthless piece of rock you want for your wives or daughters to "sustain the tradition".
If social convention required 1 pound of flesh taken by the knife on a living human, would you insist on it, for the sake of the tradition? (I fear many would - after all, it matches the 1,2,3 requirements)
If social convention requires a diamond, which you know very well will cause war, death and misery, and if you did not say yes to the previous question, why are you insisting on it?
It strikes me as illogical, inconsistent. Either you believe that human life is more important than tradition, or you don't. I can understand diverging opinions, I can hardly understand inconsistency in a system of belief, so I'm very sad to see intelligent replies advocating this 1,2,3 argument while missing the huge downside #4 is.
Maybe someday the sale of things containing "natural diamonds" will be banned - just like the sale of things containing bald eagles feathers.
IHMO, it should: as much as I love the market and freedom, sometimes externalities are just too big to be ignored - especially when there is also a monopolist in action, and perfect substitutes like man made diamonds.