I think the difference is that diamonds are inherently a luxury good.
I don't think that Michelin-starred restaurants or families who buy organic grass-fed beef are going to switch to synthetic meat anytime soon.
But, unlike diamonds, the vast majority of the meat market is cheap, price sensitive, and commodified. I think a two dollar synthetic meat burger is a much easier sell than a twenty thousand dollar synthetic diamond.
A huge amount of change is possible even if synthetic meat gets zero traction at the premium end of the market.
However, You can see the same debate being played out around genetically modified foods. Fear is being created about the products. As opposed to diamonds that are worn on the outside, these are things being put in your body. I think it is fair to expect that the PR campaign from entrenched food companies will be significant here.
It's really unfortunate, because the diamond industry is notoriously evil (blood diamonds, De Beers, etc), and science is awesome. We really wanted a "science diamond"
If you can't tell the difference, how does it impact signaling value? If you are optimizing for signaling value, synthetics are better since you can afford a larger and clearer one.
Pay less for a synthetic and admit it, and you've signaled a lack of sufficient wealth to buy a real diamond.
Pretend a synthetic diamond is real and you're deceiving people.
Either way the synthetic diamond is signalling something undesirable (to the target market for diamonds) precisely because it costs less.
You can see the arguments being very similar here with animal cruelty, purity of the food and pathogens, etc. Synthetic diamonds don't have the flaws of regular diamonds, much less expensive, don't have the same toll on humans and our planet. Yet, the diamond industry has positioned them as not real and most people will gladly pay more for the "real deal".
I am optimistic that there is an inevitability to this market, but the first generation of start-ups are going to bear the additional cost of being the educators. It may be decades until the "educator tax" has been paid. From a product perspective this makes for a very unattractive market. The opposite dynamics of network effects. Where the early entrant has significantly higher barriers to entry than later entrants.