I'm saying unlike other clinical fields, psychology is a grey area. It's not like you can take a blood sample and analyze it under a microscope to be completely certain of the diagnosis. Instead, you just observe and assess a person based on a pattern of behaviour.
Yes, people agree there is a disorder based on certain character traits but the diagnosis can be elusive.
For example, a psychopath could fool even the best experts that he/she feels empathy. The same way a sociopath could act normal and you would never know. However, narcissists are easy to identify.