I haven't seen any study suggesting eating vegetables is cancerous but have seen a few from meat and processed meat (studies from the WHO). I'm not vegan, but meat is 30% of my diet. If vegetables are that bad in nutritional value, why can you survive being vegan and just taking vitamin B12 complements?

I think using palatability as a way of measuring nutritional quality is not going to help you in the context of a society raised on ultraprocessed foods, because sugar, salt and other chemicals give taste to food without giving it nutritional value.

If vegetables don't give you as many calories as meat and as you say: "...any human wasting energy collecting and digesting food that doesn't have calories and macronutrients (vegetables) would be quickly weeded out", why there are so many animals still alive after millions of years eating plants (some of them eating many kilograms every day)?