Can you explain why this situation is any different than regular meat? I.e. Fish immune systems don’t stop parasites from being present in the meat, flash freezing is what kills the parasites.

Parasitic worms are huge, complex multicellular animals that co-evolved to sometimes survive the immune system response to their presence; Freezing kills them because they are huge and the scale of ice crystals severs important body parts. Living bacteria, living fungi, spores from these, viruses, and importantly heat-resistant toxins produced by these, are what I'm worried about.

One of modern humanity's oldest activities is fermenting carbohydrates in large bioreactors into alcohol, yogurt, and pickles, but there are a lot of things that turned out not to work in that history.

When we try to fabricate, say, monoclonal antibodies using large cultures of multicellular tissues for pharmaceutical work, the price ends up coming out to millions of dollars a kilogram.

I am implicitly skeptical of the protocols of a protein tissue culture that has to be produced at the ~$30/kg price level.

Could you eat it and not die? I'm sure!

But could you feed people with a billion meals worth of batches and have nobody die? I'm less sure! My understanding is that tissue culture failures are frequently the bane of a biologist's research program.

This obviously varies by animal, but some meats are safe to eat raw or undercooked if the animal was healthy because the meat doesn't have lots of pathogens inside it. Flash freezing won't kill bacteria or viruses that the immune system of an animal might.

Fish immune systems sole reason for being is to stop parasites from being present in the meat while the fish is alive. They're literally swimming through a soup of arthropods, plankton, algae, bacteria, and viruses that would love nothing more to turn their meat into more of themselves. There's always a bigger fish that is trying to eat them, yes, but the smaller critters want to eat as well!

Freezing doesn't kill the parasites, it slows the clock that started ticking when the fish was killed. It's not pasteurization, like what's done to canned tuna. It just slows the clock when you refrigerate or freeze the fish, but does not reset it to zero. And of course, if you're eating fresh fish that was healthy when it was killed, there's no need for an intermediate freezing or pasteurizing step.

This situation is different because the "clock" starts when the cell cultures are removed from the donor salmon. The whole blob/tank/plate/catalyzing surface (I'm not sure what the design is, I wish they had more documentation) on which the product grows for the whole time that the product is growing is vulnerable to a single bacterium that would grow out of control, like an immunocompromised human might be killed by an ordinary illness that most people would shrug off in 24 hours.