Progressive thought has moved on from Soylent Green to Coma to Death Becomes Her. All that advanced under the influence of Night of the Living Dead.
As to 15% of Americans and Europeans endorsing it, I pray it is that small, but theres cause to doubt it. Recipients of donated organs may be too ready to accept a conscience numbing story as to the origin of their new body part. A scraping of the organ and DNA test could verify the storys veracity. Could their life extension be the product of far Eastern notoriety? Uh, STFU.
Bottom line: Soylent Green seems apropos for some reason because cannibalism is not strictly a gastronomic experience any more.
So here's your soundbite General Sulla.
True! There is an old SF theme that as organ transplants grew more common it will be accepted that executed criminals will have their organs ‘donated’ to ill folks, and that this will lead to the death penalty becoming more common, extending even to traffic violations.