Suzanne O'Sullivan is an excellent, compassionate and thoughtful writer so I will be buying this book - thanks for the share token OP.
The comments on this thread are completely supportive of her point about people seeking diagnoses as sn imagined unadulterated good. It is incredibly difficult as a Dr to have a nuanced conversation about this. There's a really old well designed study showing patients diagnosed with high blood pressure, compared with those who had the SAME BP but no diagnosis had increased number of sick days (not related to meds).
Diagnosis is absolutely not a neutral act. Sometimes it is helpful, sometimes it is hindering (though the diagnosed person might not think this) - it is complex and should always be a considered conversation.
And YES you absolutely can overdiagnose cancer. Prostate is classic, but true of many - cancer is not one disease and it is not known, for example, how some breast cell changes ('cancer') behave. Most people (both pts and drs) want to err on the safe side, but that may end up causing medical harms as well as an illness identity.
Please do not dismiss Dr o'sullivan or the Telegraph; this is such an important subject and she is a good person to tackle it