On face value the answer to whether or not eating oysters and other bivalves (such as clams, mussels, and scallops) is vegan would seem obvious. They’re animals so of course they’re not, right?
The argument is that because they don’t have a central brain it is unlikely they’re able to feel pain. There’s also no evidence that they possess consciousness like more advanced animals do. So, if they don’t experience pain or fear is there still a legitimate moral concern about eating them?
There’s two main concerns that come to mind. First of all, there’s the issue of the slippery slope. Before I was vegan my favorite food was seafood. I ate it a lot. Opening the door to embracing cognitive dissonance could easily spread to other types of animal products over time because, let’s be honest, most people don’t go vegan because they don’t like the way animal products taste. People who have been vegan for years revert back to the way they used to eat despite everything they know because they miss the taste, convenience, etc. Honestly, for most of us, if you open that door unnecessarily you’re just asking for trouble.
The other point I’d like to make is that we don’t know everything. It wasn’t that long ago that it was commonly accepted that fish didn’t feel pain. Now we have evidence that suggests that they do, although there is definitely a lot of debate remaining on this subject. It’s possible that these creatures are more complex than we are able to understand at this time. After all, while they don’t have a brain, they do have a nervous system. They’re even able to respond to stimuli. (Keep in mind this doesn’t mean anything in and of itself. Plants do this as well, for example.) If we’re willing to make the commitment to be vegan, why complicate things? If it’s not necessary then you’re just convoluting your stance on animal rights and possibly sabotaging your chance of long-term success.
I’ve said before and I’ll say it again: I’m not a doctor or nutritionist, but even if I was I doubt I’d have the confidence to claim that absolutely everyone can thrive on a plant-based diet. It’s possible that someone interested in veganism, but struggling with health issues that make it difficult, could limit their animal product consumption to bivalves. In this instance, I think it’s a matter of doing as little harm as possible. There is value in acknowledging that there is a hierarchy of sentience. Otherwise if someone is in a position where they have to eat animal products for the sake of their health, there is no distinction between eating an oyster or pork. However, we know that pigs are highly intelligent beings that inarguably have the ability to experience fear, pain, and to suffer. Eating an animal that cannot experience any of those things (as far as we can tell at this time) is a more ethical decision.
Some people may be concerned with nothing more than maintaining the accuracy of the vegan label regardless of whether or not there is an actual moral issue. However, I do think these are legitimate concerns for anyone considering eating bivalves. In the end, I think if eating them will increase your likelihood of eating other animal products then you should abstain. But, if you’re in a situation that eating them will decrease that likelihood than there is an argument to be made.