WWW I think comparing the hours building instructor , who only instructs because the airlines are not banging on their door, to either doctors or sweat shop workers is to miss the point. You are obviously clear in your views that the poor suffering instructors are subsidising the PPL training of others. This throws up two issues:
First, presumably those instructors who themselves had a PPL in a past life were similarly subsidised, if that is the correct interpretation and;
Second, surely it is arguable that it is the PPL who is subsiding the instructors hour building costs. As the only reason the reluctant instructor instructs is to stay flying and to build up their hours to be more attractive to the airlines, presumably in the absence of the instructor job they would either, not have the hours, or have to go and pay for them themselves. It is therefore a mutually symbiotic relationship.