Well....I would first argue with your inclusion of athletes/rock stars/lots of actors being placed in the "professional" category. They may not be amateurs, but their jobs don't really qualify them as professions, according to the standard definition, obtained from Wikipedia:
A
profession is an occupation, vocation or career where specialized knowledge of a subject, field, or science is applied.
[1] It is usually applied to occupations that involve prolonged academic training and a formal qualification. It is axiomatic that
"professional activity involves systematic knowledge and proficiency."[2] Professions are usually regulated by
professional bodies that may set
examinations of competence, act as an
licensing authority for practitioners, and enforce adherence to an
ethical code of practice.
And the market speaks. There is the economic mechanism for these people to obtain these astronomical earnings. Fans, patients, and clients are supporting them, with no questions asked and no complaints about how much it costs to access their services, talent, etc. (except for those who can't afford the cost of medical care).
But I would be very intrigued by how many people would go into some fields, including law and medicine, if salaries were capped. It may not be a fair argument to compare doctors earning what teachers do since there are so many more years of schooling required. I do think there might be some who would go into professional fields like medicine and law since there are people who do so in countries where they are not compensatd well at all.