Not eating animals does not immediately get you to vegan. Human body is not designed for a vegan diet. However, eating animal products that don't kill the said animal, (milk, cheese, yogurt, eggs etc) is sustainable and feasible. Of course factory farms, which encourages over consumption, are not the way to go.. Not everything needs to be eaten daily. Also, things like 4 egg omlet with a mountain of cheese etc are an abomination. Consume in moderation and the production won't be a burden on the planet.
The human body also isn't designed for vaccines, going to space, or doing math. Somehow, when we need the human body to do something, we find a way to make it happen.
I appreciate the point you are making. Humans have ingenuity, for sure. But I have to disagree on a finer point. We do not know what the long term effect of vegan diet is. Supplements may work to an extent but may not be complete. To contrast with your examples, vaccines work with the body's natural defences and even there long term testing is needed to uncover unexpected side effects. Going to space is risky and even after controlling for all we can think of disasters happen. Not sure all of human race should embark on a risky mission of vegan diet without fully understanding the long term consequences. Morally I am ok with animals like cows and chicken bred for milk and egg. Your threshold is different and I get that too.
