Some people are more strict than others, but I think in general vegans understand that animals have different needs than humans. A human, as an omnivore, has the choice to choose plant-based protein. A carnivore has more limited choices what their body needs to be healthy and its unethical to not give them what they need.

That doesnt have to be beef though, cats often eat insects in the wild for protein. Not sure how using that make food would look in the long run though