I would think you could do with some explanation of why people aren't genetically programmed to avoid eating X. Assuming that it has been around for an evolutionarily significant period. Some explanations could be that it interacts with something in the new diet or that humans have lost a gene required to process it.

Some taboos have survived well into the modern times due to innate, noncultural instincts. Take for example avoiding incest and the taboo around that. That is still alive and well. We could probably screen for genetic faults, or have sperm/egg donations for sibling couples nowadays but we don't see many people saying we should relax that taboo.

Edit: The instinct is called the Westermarck Effect and has been show resistant to cultural pressure. The question is why cultural pressure works to break down other taboos, especially with regards to mating/relationships, which we should be good at by now. We have been doing them long enough.