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!
In Taiwanese cities you have public bathrooms within a radius of a 10 minutes walk, and they are as clean as hotel bathrooms, and for free. People in Taiwan leave bathrooms clean as they found it, and there is no vandalism in Taiwan. It works if the society is healthy, teenagers and adults of all social classes following common sense of being nice to others and keeping things intact.