There is, in fact, an excellent charity called Doctors Without Borders who are all about doctors giving their labour force for much less than society would gene

There is, in fact, an excellent charity called Doctors Without Borders who are all about doctors giving their labour force for much less than society would generally value it for. They're not the majority of doctors, just like the majority of software engineers are not charitably motivated open source developers. They are, however, doing immensely valuable work serving people who would otherwise not have a shot at getting any sort of proper treatment.