naming photo subjects

You cannot disable the face detection completely. Photos is automatically scanning for faces, because it needs to recognize objects to be able to classify the photos according to the scene type. This is used by the search panel and by Siri to find your photos, and to create memories.

You can just ignore the face detection and face recognition and never name the faces.

in the newer versions of Photos it is no longer possible to remove automatically detected faces, you can just disable the display of the faces labels, as explained by Mark.

You can turn off the display of face names with View > Hide Face Names.

If that's not what you wanted, please explain in more detail.