It is amazing at the FI's who get there knickers in a twist over people putting something back into aviation for free. If a student wants to fly with a specific Instructor it is their choice, if that Instructor does it for free then it is also there choice.
I don't see the issue as it is not taking bread from there mouths. I had the same issue when I started teaching, I don't need the money so I wanted to put something in for free to try and help GA. I got grief, so now I everything I would earn is donated directly to charity, comic relief, stroke and cancer research.
What tosh, Airline pilots and others teaching for free is nothing to do with the reason FI's are so poorly paid. Fi's are poorly paid because the vast majority of them are seen as hour builders not interested in the long term future of the school or the student. The training industry is so tight on margin and the flying population unable/unwilling to pay. And how do you classify poorly paid? £13 an hour is more than twice the minimum wage. You don't look at the checkout staff at Tesco or the bus drivers etc as being so "poorly" paid and they are on far less. Oh of course taking a few "professional" exams makes you better than them?