I would say that the problem is not that much people eating too much protein, it is rather people eating the wrong meats (from the crap fed animals) and underactive people.
Doing exercise everyday is not something "extra" that you add to improve your health to a higher degree, it is something that should be the norm!
And while it was not easy to catch wild animals, it wasn't that hard for group of social humans, and just killing one big wild animal is enough to feed a lot of people, and they had means to preserve the meat (freezing, fermentation).
And you are right about seafoods, maybe in a couple dozen years, it will be too toxic to even be edible... We're killing the earth from every angles!