The reason I don't eat oysters as a vegan is because carnists are always looking for wedge issues and loopholes for why their favourite treat animal is actually fine to eat. When I'm out with friends and someone asks "you don't even eat oysters?" I say "no." specifically so that they don't get to say "oh well carpoftruth the vegan eats oysters but they're a super vegan so it's probably still fine for me to eat fish and look down on the steak eaters." Fuck that, I'm not giving them that satisfaction. They can carry their own water.