Soylent Green is an imperfect analogy--at least as long as our human-flesh-powered prosperity machine keeps humming. What we've got is a sort of combination of A Brave New World and Soylent Green. Life is pleasant in every respect to the point that moral argument against it is difficult--do you not like happiness? There is something deeply unhuman about it, but it is nearly impossible to see or articulate from within that life.
Of course, introducing a secret dark side makes the book less interesting as a moral puzzle, but (at least if you believe in Original Sin) makes it more realistic. These things always have a dark side.
H.G. Wells' Time Machine is another suggestive analogy. We Eloi have a pleasant life. Nothing to complain about. Oh, but we're basically cattle being fattened for slaughter. The difference is that the human race isn't divided (yet?) into Eloi and Morlocks. With apologies to Solzhenitsyn, the line separating Eloi and Morlock cuts through our own hearts.
There are probably more analogies. Cannibalism was once a go to symbol for horror and barbarism--possibility in our future due to the degeneration of Christian society (Soylent Green, Time Machine, Heart of Darkness). Now, it's less and less of a symbol and closer to reality.
All we need now are some sexual degenerates (like Armin "Der Metzgermeister" Meiwes) claiming cannibalism (consensual, of course) is a human right. Then we can frame opposition to cannibalism as anti-science and anti-gay.
