Psycho?

[M forever]

I don't understand that there's a limit of "depersonalization," and if crossed, it steals from other spheres of life.  But I guess there are people with Depersonalization Disorder that stops them from listening to music or having sex.

Yes - Sean, for instance.

[Scriptavolant]

Maybe psychologists think they're obvious to anyone with common sense.

Usually is common sense which believes that psychological concepts are obvious to anyone. They aren't.
The point is, not a matter of quality, but of quantity. One could have (or feel like having) all of the symptoms listed in any category of mental disorder, the point is to ascertain the gravity and pervasiveness of such symptoms, as you pointed out.
Problems with precise definitions and measuremnt are common in disciplines as psychiatry, clinical psychology and psychoanalysis, but for the sake of truth one should not confuse these disciplines or mix them up with psychology as a whole, which is a vast field of research including very different methodologies, theories and objects of research.