Well, I can say I've been a vegetarian my whole life and vegan (and I'm talking about a healthy vegan diet...no functional food...) for 14 years... And I have no health issues 🤸 So, I disagree with that: we don't actually need meat to thrive.
All plants have all the essential amino acids. And that's where the big confusion lies. People think we humans need a lot of protein. But that's not the case. We need all the essential amino acids so our body can build proteins from them. When we eat proteins, our body has to break them down first so we have the amino acids so the body has building blocks. I also believe it's way better to eat fat and oil from the whole seed and nut etc, then just the extracted oil.
I also don't think there is a humane way to kill... Killing means suffering and stress. Dying is not killing... If a cow is old and ready to go, the meat will probably not be enjoyable. As the process of dying means, the body is already in the process of decomposing. 

But I know, that this discussion is endless 😢