Our ecosystem dying is also pretty suboptimal.

You can do a keto diet without meat.

But the human hand was designed to hold a banana.

Not quite true, but cooking becomes quite a bigger challenge.

But mainly, beef and meat is not the same, cattle needs way more ressources than chicken for example, or well, insects.

There are other sources of meat.

Also dairy is not a meat.

Not all meat is steak. Reducing and/or exchanging beef for other meat sources can at scale already make a massive difference.

Chicken, for example, produces 10% of CO2 per kg of meat compared to beef.

There is no health reason to eat meat. You can get your B12 elsewhere.

Ridiculous comment. The human body is not designed at all, and is very much capable of surviving without milk and meat. It's not even very hard!

And yet the most populous country in the world has an enormous contingent of people who do not eat meat (on the order of hundreds of millions).