Spoiler alert, in case you haven't seen the 1973 movie Soylent Green {wiki}. Soylent Green is made of people. However, you have to remember that the world in the movie is horribly overcrowded and underfed. After all, it is set in 2022!
First, a quick recap: In the movie, the earth is overpopulated and over-polluted. Global warming is in full swing and even rich people have to eat crummy food. The government hands out rations of Soylent products, which are awful, flavorless cubes and loafs of “soy” (actually plankton but really it’s irrelevant cause it’s people) foodstuff that look like red, blue, or green Play-Doh. When you die, you go to a death-a-torium of sorts where you pay a small fee, then watch a really pretty movie filled with scenes from nature and peaceful music. You die quickly and painlessly from a colorless, odorless gas.
Then your body is shipped off and turned into Soylent Green which everyone loves to eat.
Would you eat Soylent Green under those conditions? How about in other science fiction scenarios? Several are spelled out at Science Not Fiction, where you are asked to leave your thoughts. Link
And if everyone else was doing it, you probably wouldn't even find it yeuchy. It's a monkey society.