Why do we obsess over fish appearance?

Well to be honest, the entire reason people began keeping fish is for their beauty, fish aren't like dogs or cats, they have VERY limited ability to learn, communicate, recognise you, be your "best friend"... There really would be no reason at all to keep fish unless we ate them or we thought they were pretty. Regardless of the REASON you treat the illness, as long as the fish gets treatment, it's a perfectly fine relationship.