Why are people shocked at the thought of a human eating a human, and yet think nothing of a human eating a cow, or a lion eating a human?
Cannibalism - human or animals eating the same species - leads to diseases. There's a reason why we're programmed to be repulsed by it.
"Diseases often have trouble jumping from one species to another. The closer related to you your food is (evolution wise) the smaller the gap the disease needs to jump. This is why eating bushmeat from apes is more risky than eating some less closely related animals.
The above is true especially for viruses. Parasites are another problem. One thing that has been big in the news are prions.
Prions aren't really living things at all. They are just certain types of proteins which cause the proteins inside of you to become like them by their mere presence. In particular the prions everyone is worried about are ones that are inside your brain and nerves. If you eat another humans brain who has such a prion disease you will become infected yourself.
Normally this is not such a big deal as people aren't in the habit of eating each others brains.
However in cultures where cannibalism was practiced, such disease can become a problem. One example is Kuru also called the laughing diseases which used to be found among cannibals in places like New Guinea.
Another example is mad cow diseases which became a problem when people got into the habit of feeding cows the remains (including brains) of other cows.
In fact mad cow became such a big problem that enough cows with it ended up in the food chain to possibly infect humans despite the species gap. Creutzfel-Jacobs is what the disease is called that many think is what happened if you eat cannibalistic cow brains.
Kuru is a type of
prion disease causing spongiform encepalopathy (literally bits of your brain die off until it looks like a sponge with holes in it everywhere). We're not exactly 100 percent on the causes and exact chain of events caused by prion diseases, but I'll give you a rundown of the most likely scenario. Transmissible spongiform encepalopathies (TSEs) aren't carried by bacteria or viruses - they are essentially a disease caused by the misfolding of a certain protein. This is bad because protein shapes are vitally important to their function; if they misfold, they don't work. What happens is this - by eating the brain matter of an infected person, the victim also ingests the misfolded protein. Here comes the bad part - this misfolded protein comes into contact with and triggers the misfolding of the victim's normally folded proteins. This causes a cascade of misfolding proteins and eventually large scale tissue death (the brain-looks-like-a-sponge part)."
Anyway, I don't think you made this post because you believe that eating human flesh is morally equivalent to eating animals - you're just trying to be controversial for the attention.