Maybe not, but whether it's ok to eat animals does, and so does consistency. If the criteria you previously gave is really the criteria you believe makes it ok to kill/eat something, why aren't you willing to say it's ok to eat humans who meet the criteria?
I'm resistant because it's so hard to do a prudent level of testing on a single individual. If you have some method of determining that there is no shred of full-functioning in their brain, that they truly have the mind of a lower animal, that you can show this to others, then okay it's viable to eat them.
But it still gives a misleading impression when someone hears you ate "a human".
