A while back I learned that a "heel" derived its meaning from being a contemptible wrestler, someone you weren't supposed to cheer on. This all changed with WWF/WCW in the 90's when they realized the audience loved their heels more than their babyfaces. Take for example Roger Atlas / Arkansas (Contemptible in a good way of course).
Roger Atlas (weekendwrestling, Muscleboywrestling)
Arkansas (thundersarena)