The author states,
"And perhaps most crucial, to what extent do professionals have a collective duty to ensure that their profession provides nondiscriminatory access to all professional services? "
Amendment XIII
Section 1. Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction.
Amendment XIII pretty well sums it up on this question of whether a "professional" has the right to withhold "services" for whatever reason.
Thank you. Great info.