Unconsciously, it's because having hair means you're hiding your features and you are therefore untrustworthy. On another level, at least for facial hair, a shaven face shows you can take the time and effort to try and look like a civilized member of modern society. The same can be said for shaving your legs, armpits, pubic region, etc. but that's more for visual/physical appeal than anything.
Unshaven isn't really a professional or socially acceptable look, I prefer unshaven though
Society does not make sense when it comes to preferences since it pretends to have things that are generally likable when in fact it simply forces this fact down your throat by judging and punishing those that feel otherwise. This control through fear is actually quite similar with the definition of terrorism.
Plastic look is in vogue