I agree with you about what we evolved to eat. But I don't agree with you about cows being environmentally friendly. Everywhere in the world they mostly graze land which used to be forest. Here in the USA that is definitely true. And I have a great example, in fact. I live in Kelseyville, which is in Lake County. It's named for a guy who enslaved, raped, and murdered the locals — it's a bit living in Hitlerville or Santa Torquemada. This town has a whole bunch of walnut trees, and indeed it used to be one of the biggest walnut producers in California. The US government paid people to plant these trees, and so they did. But first, they cut down whichever oaks hadn't already been cut down to make room for cattle ranching. Part of the idea, of course, was to eliminate the natives' food source. They ate acorns. You can live on those, but you can't live on walnuts alone.
So yeah, in places which naturally tend to pasture, grazing cattle is perfectly environmentally friendly. Problem is, those places are in the minority. Most places tend towards forest, if you give them enough time. And most of the places where cows now stand, trees once stood. Many of them have been recently slashed and burned.
I love me some meat, and I eat as much as I can, but let's not pretend that it's more environmentally friendly than vegetarianism. And sadly, cows are pretty much the worst. The methane of their flatulence is a significant greenhouse gas and the deforestation their existence implies is part of the problem with global climate today.