Very true. Zero symptoms is a nice thought, but thinking that treatment is inadequate if it doesn't achieve that is dangerous for all the reasons others have brought up.

My symptoms are probably 75-80% controlled on my current meds. I no longer have to deal with mixed episodes and the depressions are shorter and no longer make me suicidal. I consider this a huge improvement and can cope with the depression I still get sometimes. I would not want to continually be trying to increase my meds seeking some zero-symptom ideal.