The bourbon manufacturing process is as simple as moonshining... Only people have grown up with it and think it is harmless and tasty. (The aging process improves the whiskey properties, of course).
On contrary, rum is distilled in a pretty sophisticated way; I'm talking the white and golden varieties. (Fermentation of sugars never produces any poisonous methanol).
Distillation of vodka is a miracle of engineering, leaving almost totally pure alcohol and water and removing nearly all poisonous chemical compounds. The traces of the impurities define the vodka character. For instance, Absolut is the clearest vodka known to me, just pure ethanol and water. It can be drunk by big glasses before you drop