There seems to be two issues with cadet schemes. Some people seem to feel that cadets that graduate from these schemes lack suitable experience (if that is the case, why aren't you as equally concerned about cadets who graduate from military training?) and others see the schemes as ways for operators to reduce Conditions of Service.
I think it is the reduction of CoS that is the real issue. It isn't just happening in aviation but in other walks of life too. A friend of mine worked as a "volunteer" (to get experience) for 6 months (Mon-Fri 9 to 5) to get a $45k a year job. I had the same opportunity but objected to work for free. He is employed and I am not. I can't blame anyone for taking opportunities like that (or the cadet scheme) if they want to. However, the companies that take advantage of people (who work for free or "buy" their own jobs) would be the problem. Surely there is some legislation somewhere that prevents workers (or cadets) being taken advantage of like this? If not, why not?