Author has a very hand wavey attitude toward prions.

There are many kinds of prions capable of causing spongiform encephalopathy in humans and likely others which are currently undiscovered. To suggest we continue eating brains because some people "probably have an immunity" is irresponsible. To my knowledge, evidence of immunity to prion disease has not been scientifically established.

Edit: Furthermore, prion diseases can have long incubation periods (years or decades before symptoms manifest), making them extremely difficult to detect in normal clinical settings.