This is a crock of shit.
We have Canine teeth for a reason.
We are bipedal to better see over tall grass for hunting/protection. As well we are natural endurance runners meant to chase our pray to exhaustion, plants don't run away.
If we were herbivores we would have stomachs better adjusted to a plant based diet, like a ruminant digestive system. Majority of the energy in plant matter is stored in cellulose which humans cannot digest.
Our eyes, one of our best traits, were evolved to react to movement and to be able to differentiate between shades and colour which improved our ability to hunt. Herbivores don't require keen eyes like a hunter.
One of the most common allergies are tree nuts/legumes which are the best source of protein for a vegetarian diet. Very few people are allergic to meat.
B12 is a vitamin necessary for proper brain and nerve function. The best and one of the only ways to get B12 is, you guessed it, meat! B12 requires bacteria to synthesize it which can be obtained by the consumption of meat/dairy products that host these bacteria. If we did not consume meat and dairy our ancestors had to ingest their own or some other animals shit, the only way to naturally obtain b12.
Tooth decay, and other diseases along the digestive tract were virtually unheard-of before farming and the consumption of grains. Before the consumption of grains began all humans had the physique of Olympic athletes. Farming and grains made us short, fat and sickly.
I could go on but regardless, you should be thankful that our ancestors were omnivorous. Our diets adaptability allowed for mankind to reach the height it has in modern days and allowed yourself to enjoy the luxary of eating a vegetarian diet. You do not have to worry about food availability but our ancestors did, meat was a year round source of fat and protein. As well there is a significant increase in intelligence and brain development from carnivores to herbivores so you can be thankful for that. You didn't have much choice though because we have evolved from a long line of carnivorous reptiles that evolved into carnivorous/omnivorous mammals. Humans have been carnivores/omnivorous for much longer than the 200 000 years of recognized human existence. So yes there are societies of Vegetarians through out history, but no, humans are not naturally vegetarian. We are naturally omnivorous and thankfully so. If you want to cut anything because we are not built to consume it cut grains, it caused the gradual downfall of or society. Maybe we can return to tall, disgustingly fit apes if we give up the waffles.