Wouldn't such a company be out-competed by a company that combines artificial diamonds with donations to the rare diseases in cute puppies fund? More warm fuzziest per dollar spent.

Also, both would have to compete with much, much cheaper artificial diamonds, and so likely could not capture the 90% premium. Plus, the signaling value of having an artificial diamond is much less if some are cheep and other are not. Branding doesn't help a small charity diamond startup much, since the people their customers are trying to signal to haven't heard of them. You might be able to do it with a major name brand jewelry company, though, but they'd have an incentive to maximize warm fuzzies/$ and minimize donation amount.