To be fair though, are people who practice alternative therapies even meant to be diagnosing disease?
In my work as a Physical Therapist and Sports Massage Therapist, I would not say that I am diagnosing disease - musculoskeletal dysfunction/imbalances yes, but not disease per se. Whilst at university, I studied all the required medical modules and know when it is unsafe to work with someone and when to refer them back or on to others.
I would have thought that other practitioners would have training in this also? The taking of a case history is one major factor in highlighting problems such as this. I also include other assessments for myself, such as postural and range of movement exercises, but then I find I can get the most information by actually starting to work with someone and being able to feel what their underlying tissues are like.
After one treatment I performed, I did refer someone back to their GP and they were able to get the problem diagnosed and treated in the very early stages, so that they had no further problems. They were very grateful for this.