That is trying to play with semantics. A disorder is an illness
Semantics are important here to differenciate between different ways of dealing with it properly. People should know that narcissists/psycopaths/sociopaths cannot change to the better, because the inherent nature is not accepting any flaw. Only by knowing this other people can protect themselves by not keeping contact to them. It's the only way to protect yourself.
You linked "Mental Disorder", which can be a whole bunch of things including mental illnesses, but I'm talking about "Personality Disorder" specifically, which can almost never be cured.
The question is who we should try to protect. You can tell a narcisist to seek help for sure, but also tell others to stay away from that narcisist until he/she has changed to an empathetic being (which rarely happens). Narcisists don't see a reason to change, as they feel entiled to see other people in their lives as resources. Each of them is hurting many people through manipulation and explotation. If you meet a psycopath/sociotpath/narcisist, there's only one advice: run!