(1) True free-range poultry barely exists. By this I mean chickens 
that have been raised solely on bugs, grubs and vegetation. All 
farmers I know supplement with chicken feed. (The reason the plant 
named chickweed is named that is because chickens love it.)

(2) How easy is it to catch birds in the wild with stone age tools? 
If it is really hard, then following optimal foraging theory birds 
would not have been a staple.

(3) Compared to raw red meat, raw chicken is kind of yucky. We should 
assume that our taste buds have evolved to help guide us to what it good for us.