This is the most half-baked idea I've ever heard.

Hunter gatherers weren't fat because they didn't have the available food sources to get fat, not because of their diet. Populations were tightly bound to available calories, overeating would make someone else starve. 

Meat has benefits, but you're dramatically overstating it. Vegetarian diets are more than capable of providing the same benefits, without the risks associated with red-meat consumption. 

I eat meat cause I like it, it tastes good. I also eat Reese's cause they taste good. I'm not under the false impression either is the best available option, but in moderation both are fine. 

Your viewpoint that meat is unequivocally good is false.