So, the straightforward portion of the Pagel/Bodmer theory is that ectoparasites such as lice are dangerous (lice carry typhus and other serious diseases), and ectoparasites prefer hair to bare skin. Getting rid of hair is a good way to make life difficult for these unpleasant and dangerous parasites. It is also much easier for us to see and pick off ectoparasites like ticks if we have no hair. Primates spend a substantial amount of time doing this, to themselves and to each other. It has become, indeed, a major social activity and, as a by-product, a vehicle for bonding.
