Not pedantry. Veganism is an ethical position, distinct from carnism, which is also an ethical position. That may not be how the majority use the term, but it is possible for a majority to be misinformed. If vegans yield the term and it comes to mean “mostly eats plants, sometimes eat fish or pig or perhaps bear”, what should they call
“tries to minimize animal abuse as far as possible and practical”? Wouldn’t the new term also be eventually devoured?

Because that’s plant-based plus bacon. Veganism is an ethos, not a diet.