- patients will worry too much, and - it will cost time and money to investigate.
Both spurious rationales cooked up by an industry that is at least as hostile to humanity as it is helpful.
Nobody is deciding for themselves to do chemo because they think something looks funny on a scan. All the scan gives them is a reason to talk to their doctor, who will do all the usual due diligence before deciding on treatment, if any.
And on the flip side, I hear stories all the time of people who DO have symptoms but they get dismissed by their doctor as stress or food allergies or whatever until it's too late. Maybe if patients were armed with a scan that shows a mass at the site of their abdominal pain, there would be fewer of these horror stories.
Even if we accepted your example, there is a fundamental inconsistency, since doctors in America regularly prescribe very serious drug interventions for patients who essentially self-diagnose for being neurotic/adhd/etc.--actually a much worse problem than the one you're so eager to curtail.
- patients will worry too much, and - it will cost time and money to investigate.
you forgot one more, which is subjecting people to potentially risky procedures for things that were not a health risk in the first place.