While I do agree with most of what you said I think there is value in providing people descriptions of behaviors that they may see in other people. For example

While I do agree with most of what you said I think there is value in providing people descriptions of behaviors that they may see in other people. For example, if a relative of mine 'Timmy' suffered from schizophrenia but schizophrenia as a diagnosable condition didn't exist yet then it would be much more difficult for anyone to know how to deal with Timmy. Some might shun him while others might fully buy into his paranoia. The dark core traits have real victims so providing society with a means to identify and describe those behaviors will provide some limit to their range and impact.