In several places in Sunless Sea, there are locked storylets that require the quality Unaccountably Peckish. I'm pretty sure you pick that up from turning cannibal. (As the tagline goes, LOSE YOUR MIND. EAT YOUR CREW.) And right now, I'm staring at an option involving the Sigil-Ridden Navigator that's much, much cheaper if I'm Unaccountably Peckish, and I've seen that quality unlock a couple of minor storylets in Adam's Way and Gaider's Mourn, too.
So it looks like there's something to gain from violating one of humanity's more sacred taboos. Is there a downside to sampling Long Pig? Aside from the somewhat-inconvenient tableware?