This kind of debate is always very silly. The most important thing is that it doesn't really matter what is "natural" (paleo is a silly trend), just figuring out a way for all people to gain sufficient nutients in an efficient and sustainable manner. On this metric, the current consumption patterns of meat are not ... satisfactory. The (relatively recent) ubiquitisation of the meat + 2 veggies meal is putting enormous stresses on supply chains. Particularly inefficient are fish farms for secondary consumers and the rearing of pork and cattle; but most have their cost. The best meats tend to be shellfish, but I doubt many people will take to a clam-and-mussel-based diet very well. It is very hard to change people's behaviour unfortunately.
