It's not at all obvious that the "medical costs of today are extremely large mostly due to overconsumption of animal products". Some people blame sugar, which is made from plants. Some people blame fat, which in the modern American diet is largely vegetable oil. But human nutrition is notoriously difficult to study, so making strong claims about any specific thing being to blame is probably dishonest in some way.

This issue puts most people in direct conflict with their own cognitive dissonance: objectivity goes out the window.