"Kosher" has never been a set of objective standards. Jews have been arguing about it for thousands of years. It's not a scientific law; it's rules set out by rabbis and basically every aspect of it has been contested at points.

If you're interested in learning more about this kind of kashrut system, there's a fascinating book about the topic: "Kosher: Private Regulation in the Age of Industrial Food". [1]

[1] https://www.amazon.com/Kosher-Private-Regulation-Industrial-...