When picking out oysters to eat, provenance usually gets the most attention—which slight inlet of brackish coastal waters were the shellfish raised in?—followed by accompaniments. Mignonette? Or cocktail sauce? That oysters can be farmed without the use of massive amounts of ground-up fish as feed, as is the case with, say, salmon, and that the mollusks have the near magic ability to clean the water they’re raised in, is just horseradish on the proverbial half shell.

Writer Rhys Southan thinks about bivalves slightly differently. They are nonsentient creatures, which makes them excellent candidates—from an ethical standpoint—for eating. However, as he wrote recently for Vice, “although few do, oysters can reach 20 years of age.”

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Instead of considering seafood consumption from an ecological perspective, Southan writes that he’d like a guide that allows people to pick the seafood that’s harvested with the least amount of natural life left: “The Seafood Buyer’s Guide for Those Who Accept the Deprivation Account of the Harm of Death.”

The “Best Choices” would be those born on the cusp of death by natural causes, including many shrimp, smelt, and many species of squid, as well as the seven-figure pygmy goby, which enjoys a maximum of 59 days on this planet.

The immortal jellyfish, which ages in reverse after reaching sexual maturity, would be listed on the opposite end of the spectrum. “Eating a Turritopsis dohrnii jellyfish means depriving a creature of a potential eternity of life,” he writes. “Please refrain from eating immortal sea creatures.”

Southan was a vegan for nine years, but after he began to suffer from various health problems—extreme tiredness, dramatic nosebleeds—he decided to add animal products back into his diet. He started a blog, Let Them Eat Meat, and from that perch he’s become one of the most thoughtful, engaging critics of veganism.

“I started getting so depressed that I was kind of, like, indifferent to my own life,” Southan recalls of that unhealthy period in his life. “And that kind of made me indifferent to animal lives, so that made me think that maybe I could stop being vegan. I also had thought, ‘I’m feeling really miserable; if this has anything to do with veganism, it may be worth it to try animal products just to see if I could feel better.’ ”

He did feel better, and almost immediately, but vegan friends—including someone whom he convinced to give up animal products—didn’t take so kindly to the changes in his diet. Despite the kind of delicate ethical reasoning that’s behind Southan’s years-left-on-Earth approach to eating seafood, the ideology of veganism tends toward the binary: You’re in or you're out. The sentience or life expectancy or care of a given animal that might end up being your rigorously, ethically considered dinner doesn't really factor into the equation.

As Southan puts it, “If you’re a Marxist or something it’s okay to work at a corporation. You don’t have to necessarily behave like a Marxist to believe in Marxism and call yourself one.” But when it comes to veganism, context and action are tantamount to the ideology. “Veganism is this kind of belief that requires you to act in a certain way, and if you no longer feel that you can act in that way, you then basically have to renounce the beliefs,” he added.

When someone renounces the belief, like Jordan Younger, the blogger behind The Blonde Vegan, Southan says “what vegan bloggers usually pick on is, they’ll say that whoever was the vegan who’s now an ex-vegan has done veganism wrong.” Rather than trying to find balance within the lifestyle, be it through supplements or eating more highly processed vegan staples, such as tofu and wheat gluten, they simply return to eating meat—and that’s considered a cop-out.

But consider the oyster: If you slurp down half a dozen, you’ll get more than double the amount of vitamin B12 you’re supposed to consume in a day. They have plenty of omega-3 fatty acids, which people so often turn to more ecologically sensitive salmon for, and plenty of minerals, namely zinc. If some people, like Southan, cannot be vegan and be healthy, then why not make a principled, ethical change and introduce oysters into your diet? Their life span is on the long side, but beyond that, eating them presents relatively few moral quandaries. Southan cites one vegan blogger, “who is not technically vegan because she eats mussels,” who has argued that the shellfish could help make a vegan-like diet possible for people who are experiencing health problems.

Similarly, the moral debate among omnivores is becoming more nuanced too, and it seems that there's a gray space developing between people who are vegans—save for the stray bivalve—and those who eat a grass-fed burger here and there. “Certainly when I was vegan and then giving up veganism, it didn’t occur to me that there was some way to eat animals that might fit with vegan ethics,” Southan said. Despite the ire he and other ex-vegans have been subject to, having writers like him explore the gray area, bringing up things such as the life span of seafood, makes the debate far richer.