Any “humans are supposed to eat…” Argument is immediately wrong.
From an evolutionary anthropological standpoint, humans aren't really meant to do any specific thing. We are insanely adaptable, which is why we started eating meat in the first place. The human gut cannot process raw meat. So we learned to cook it until out bodies and teeth could handle it. Same with clothing: we've modified it to keep us safe in cold or heat or rain or desert. Adaptability is the whole human thing, really.
But that's the whole fucking point. We adapt to what we have to. We thrive just as well on a fully vegan diet and morally we should. We have variety to the shapes of our teeth so we are capable of surviving on any diet. But in the developed world we don't need to worry about just surviving. So meat is completely unnecessary. I could be fully nourished eating dogs every day for the rest of my life. Why won't I? Because I don't fucking have to and it's horrible. Humans don't require meat. Dietary wise, we never have.
*Obviously other vitamins and minerals and macros play a roll in health but I'm speaking within the guidelines of surviving and thriving as a species.