It doesn't matter whether you work for a flying school or not; neither do I!
The basic premise, whether it applies to you Bose-x, or anyone else, is still the same - that whilst some people (in whatever circumstances, in whatever profession) are prepared to undercut wages by working for free, then wages rates across that market will be kept lower.
Anyone who is crusading for living wages for professional instructors should not also be accepting of those who work for free.
Cheers
Whirls