It's important for vegans and advocates of veganism (like myself) to be cautious and intellectually honest about possible health benefits of a vegan diet. I'm particularly thinking about things like how John Robbins used to do it, where he threw out page after page of correlations between populations eating animal protein and populations suffering disease burdens. That may have persuaded some people, but there are so many other factors (even just dietary factors) that could have accounted for the correlations!

The gut biome topic is hot now, but our understanding of it is so new and so limited that it's going to take a while to be confident about what would be a "good" or "healthy" biome in particular ways. It's definitely easy to change it, but still kind of unclear about how to know when particular changes can reasonably be called good or bad or beneficial or harmful (with particular counterexamples like clostridium difficile infection -- that seems bad).