In other words, the fact that we have biological systems that are achievable by breeding natural stock is a backstop against producing "food" that did not co-evolve with us. No guarantees, of course, which is why it's a heuristic and not a hard-and-fast rule, but I'd much rather have meat from living animals that have to survive than lab-produced meat that we have reductively arrived at by trying to mimic the observable properties of meat from biological organisms.
GMO presents significant challenges to this, as does clonal propagation of mutant varieties of fruit trees, both of which result in things that, while not necessarily bad, have developed outside the range of what natural variability could produce as viable systems.