@awnlee jawkingIs Soylent Green cannibalism? As far I recollect, that stuff was processed beyond any recognition, even as meat, and still triggered outrage when the processing was exposed.
There's been cultures that ate their enemies, for either utilitarian or ritual purposes (to supposedly magically gain the strength of the enemies), as well as cultures that ate their own dead, as a grave ritual if not otherwise.
Beyond social taboos, there's however good reasons why cannibalism within any species is generally not a good idea. Not only that human meat is notoriously unhealthy due to most humans lifestyle and own food choices. Even in farming there's now effort to avoid feeding cows with stuff processed from cows and similar. Beyond obvious infection risks, there's the wildcards like prions that can survive a lot of processing. Eating humans that have eaten humans is therefore especially bad idea.
When survival is at stake, the risk analysis can change significantly, but outside extreme circumstances it souldn't be practiced, even when all ethical issues are put at rest one way or another. Outrage of the folks being unknowingly fed human remains isn't unreasonable, especially if there's no clear communication that that's the last resort to keep them alive. Not to mention, it raises the question of possibility of them themselves being subsequently used as food source -- in context of the clear risks of premature death for just such a purpose.
Recycling in mystery box food replicator may or may not be presented as a remedy, but even if all the physical, epidemiological reasons are resolved with such, the ethical issues remains, in my opinion. I would expect spacefaring people to elect to dispose of perfectly good edible biomass just to avoid the collateral issues.
However, that's mostly a cultural thing. It's not unthinkable to define a society where most find nothing objectionable with being eaten, even, ultimately on demand.