(and I am in a very very tiny minority)
I wouldn't be
so sure about that, I know of a few people who do instructor for free and to be honest I have mixed feelings about it....
On the one hand why should bose or indeed anyone else conform to someone else's notion of how the flight training industry should operate....or feel they have a 'right' to be paid because they themselves have invested a lot of money in their training....or indeed try and impose their notion of 'fairness' (whatever that might be) on other people.
But more realistically the essential argument that people who instruct for free undermines wages does stand up to scrutiny and for that reason if I ever decided to start instructing I would charge even though I wouldn't need to.