If everybody were hairy, it would be considered normal, and therefore not unattractive. Hairlessness is not necessarily more attractive than hair, or fur. Ever see a naked mole rat. One ugly creature.
True. But also remember humans, and only humans, learned to use both fire and clothing to help keep warm. After those developments perhaps the need for full body hair for warmth diminished. Additionally, it's probably slightly healthier to have less hair, as there would be fewer parasites and things like that. To me it seems natural that we lost fur/hair because we really don't need it like animals do.