As an IRL vegetarian, I like to sometimes try it in certain games. It's an interesting challenge in Minecraft for instance. I'm also reminded of the fish people in Starbound, they were my favorite race and vegetarian in the lore, it wasn't forced on you but I did it anyway for fun/immersion. I honestly think BG3 would function the same way, it's a low-key lore-friendly thing to do, but not a requirement. They might even sneak in some snarky dialogue about it somewhere if you choose not to.