https://twitter.com/missmayn/status/1612892354624786444?lang...
(This is not to say you can or should ignore the suffering caused by the diamond industry)
The reason people buy sea salt (made by evaporating seawater) or table salt (made by mining deposits left from prehistoric seas), is because no one produces these things artificially. There's no good economic reason to do so when you can just dig it up or dry out some seawater: making it artificially would be more expensive.
The same economics don't work for diamonds, for various reasons.
They also mention suffering, which seems kind of hard to measure but I think it's relatively well known that natural diamonds are saddled with a fair bit of baggage in that regard (slave labour, conflict diamonds, things of that nature).
You can't easily map this onto luxury watches, but it'd be like if you could buy a watch that was indisputably a Rolex, was "equal" in aesthetic appeal to its equivalent Rolex while being cheaper and didn't involve whipping the watchmaker who built it or something. And maybe a few watch afficionados with special knowledge of serial numbers could inspect it and go "ah this one was made without whipping the watchmaker"
Thing is, there are inexpensive watches that are well-regarded within the watch community though: https://www.hodinkee.com/articles/a-seventy-five-dollar-watc...