Makes Sense
First and foremost, 1 gram does not equal 15 grams. The anon from the United States (where else?) somehow convinced himself that a diamond bulletproof vest would be too heavy because of some hilarious math that they pulled out from where the sun doesn’t shine.
Now, as for why bulletproof vests aren’t made of diamonds, you got us, anon from the United Kingdom. We know that diamond prices are artificially inflated, and if all the diamonds in every vault in the world were released to the public, they’d be a lot cheaper than they are right now. If that were the case, we could probably start mass-producing diamond bulletproof vests.