Dawkins is just pointing out that our problem with eating human flesh is entirely moral—it would require killing a human, which is immoral.

Growing genetically “human” flesh in a lab would entirely remove the moral issue. Since the entire issue is moral in the first place, and that issue has been removed, Dawkins simply points out that if you still don’t want to eat it because it’s “yucky,” then you’re being an idiot.

Dawkins is not trying to get everyone to eat each other. He is simply pointing out the role of morality in taboo, and how our mind does not always operate logically; we tend to keep taboos, even after the reasons we held something taboo in the first place has changed. He is obviously not advocating murdering and eating people.

What he is doing, however, is using shocking language in an attempt to trick people into being appalled, and it is working.