Every year for the past 35 years at least 10% of my work has been charity. Essentially all doctors do charity work. We consider it an important part of being a complete physician.
The difficult part for a surgeon to do free surgery is that the facility has to be paid and anesthesia has to be paid. If your surgeon is doing truely free surgery he has paid these fees for you and it is not just a matter of him waiving his fees.