I don't think it is necessarily that they aren't afraid of human scent, but more of how much or how strong the scent is. I have had deer walk down the same trail that I just walked down an hour earlier and act like nothing is wrong. Hell, my dad, last season, had a deer sniff the ladder he used to get in his stand just 15 minutes prior and never got spooked. I believe that we get a little carried away with how much scent we leave behind and how much we give off. Although, it never hurts to be overly cautious.