Like you, I am not as confident as some of the other commenters that a diagnosis is beneficial in all circumstances. The issue is not whether mental health disorders exist, but the difficulty in diagnosing them accurately and treating them effectively. Their definitions are nebulous, the symptoms are subjective, and some of them only exist within a certain social context. With a diagnosis, a person might find a treatment, or may become resigned to being a certain way. Subjective symptoms might arise as a result of belief in the diagnosis, thereby confirming it. Treatment options are often of doubtful effectiveness, and those that are shown to be effective are generally very blunt instruments. The fact is that our understanding of the human mind remains primitive, and we much approach this subject with humility.