An actual slave would give anything to have that job, however difficult. That is my point.
and my point is that he woud still be a slave, a voluntary one, wich is the worst
No he would not. Because he can still raise a family, find a different job, move out of the country, take a risk and start a business, educate themself, and do an enormous number of things that a slave cannot do. You are using the word metaphorically and it is inaccurate and wrong.