I did not even notice that we may be arguing about something :) I have nothing to object from culinary or religious aspect but I am rather more interested in another aspect of cannibalism.
As if we think about ancient Rome or any other advanced civilization the biggest problem for it's people is insane boredom which naturally leads to various perversions and other nonsense. So I woud expect that some of those customs may have developed for entertainment purposes rather than something practically useful.
Like if we have gladiator fights we also could have some cannibal cooking competitions just like Japan had murder competitions where contestants were competing how many people they will decapitate with a sword in one minute.
Or there may be some eatery where they serve cooked breasts as some novelty food or some human cooking on stage to entertain guests.
All of that are just my theoretical speculations and I would like to see if there is any evidence to support them.

although I suspect that such rare unique events will not be well documented and all kind of entertainment is usually frowned upon by general society.
On the other hand many religious practices also may be covert entertainment for elites as it is no secret that many of not majority of famous religious leaders are some kind of perverts with very interesting fetishes which they present as religious practice to convince bigger population to participate in it.
For example famous Gandhi had scat/enema fetish and she loved cleansing little cute girls and women of course absolutely strictly for spiritual and hygienic reasons LOL

From this book i still think that most interesting part was about china as it somewhat supports my theory:)
But it is unclear why those practices did not spread to other advanced civilizations where value of human life was close to zero.

Speaking about some other supposedly historical events I just know what i heard from recent times.

there are many ridiculous tales about jews eating chidden even my grandma was scaring me that this jew who lives in the nearby house is cooking and eating children.

I heard one possibly true but story that when soviets visited some place in africa they were offered to eat a woman who was slaughtered and cooked just for them.

There was another quite unbelievable story that during ww2 there was a barber who kills his clients and later sell sausages from human flesh

And there is pretty much entire documentary movie about cannibalism during Leningrad blockade which I have seen and which may be available somewhere online.