Thank you for taking the time to provide your thoughts on this subject.
I started to add my views to the original post several times shortly after you posted yours except each time I thought I had captured them I thought of another viewpoint which negated my ponderings.
Professionals are, as you said, proficient, within their chosen vocation. Professionals no matter the work have chosen to earn their living from the results of their efforts.
To me, a professional photographer is someone who purposefully chooses to sell the images they capture. They must be technically proficient, knowledgeable, creative, and skillful to be successful, i.e. repetitively selling images.
Amateur photographers can be just as proficient, knowledgeable, creative and skillful as professionals, but their photography purpose is non-monetary. Amateurs use their images for their own enjoyment, the enjoyment of family and friends or simply for the challenge of capturing an image.
I’ll always be an amateur because my photography purpose is for my enjoyment and those close to me. I will work to increase my proficiency, knowledge, creativeness and skills with photography. Maybe someday I will attain levels equal to a professional but even then, I still will be an amateur.