Mortgage credits, student loans (and there are major ethical systems that actually consider them immoral, eg. Islam generally prohibits charged interest).... Or

Mortgage credits, student loans (and there are major ethical systems that actually consider them immoral, eg. Islam generally prohibits charged interest).... Or military enlistment contracts... There are plenty of examples where you voluntarily sell your freedom away - and the agreement makes backing out rather non-trivial. It's just not called slavery - because it isn't quite that, "voluntary slavery" is a bit of an oxymoron (who's doing the enslaving?).