I don't see this question as black and white as some.
There are so many different types of photography and markets for different types of photos that the term pro or professional doesn't really apply.
For example - Ansel Adams was a fine art photographer. He didn't shoot weddings or to my knowledge even do any commercial work. Would you consider him a pro? He studied music and probably was broke for the early part of his career.
Professors at University's very often produce fine art photos or do commercial work in addition to teaching. Are they not professional photographers because they don't make photos "Full Time."
I know many photographers who earn all of their income through photography and even their work is not so cut and dry. They sell stock, make fine art prints, shoot photos for ads, or work on portraits for politicians.
By most definitions detailed in this thread, I am a pro. However, many times I've had companies or people, who really like my work, attempt to hire me for jobs requiring photographic experience and skill that I don't currently possess...weddings and fashion mainly. While I could've taken these jobs, I think it would've been unethical to pretend that I was the best photographer for the job.
I guess my point is that professionals need to know their strengths and weaknesses and therefore set limitations on what jobs they agree to take. If I'm being paid to do something, I want to meet or exceed expectations. I would never want to let anyone down knowing that my skill wasn't up to the task. That said, you'll occasionally get an overly critical client who is impossible to please even though you know your work was excellent.
Not every pro can excel in every photographic medium. I know I'm very good in my area and if I want to add to my repertoire, I have to learn and practice enough to become skilled, competent and confident before selling it to a potential client.
I see many impressive, beautiful images posted on CR...from both amateurs and pros...which inspire me to try new things and continue to learn.